A Ukrainian man indicted in 2012 for conspiring with a prolific hacking group to steal tens of millions of dollars from U.S. businesses was arrested in Italy and is now in custody in the United States, KrebsOnSecurity has learned.

Sources close to the investigation say Yuriy Igorevich Rybtsov, a 41-year-old from the Russia-controlled city of Donetsk, Ukraine, was previously referenced in U.S. federal charging documents only by his online handle “MrICQ.” According to a 13-year-old indictment (PDF) filed by prosecutors in Nebraska, MrICQ was a developer for a cybercrime group known as “Jabber Zeus.”

The Jabber Zeus name is derived from the malware they used — a custom version of the ZeuS banking trojan — that stole banking login credentials and would send the group a Jabber instant message each time a new victim entered a one-time passcode at a financial institution website. The gang targeted mostly small to mid-sized businesses, and they were an early pioneer of so-called “man-in-the-browser” attacks, malware that can silently intercept any data that victims submit in a web-based form.

Once inside a victim company’s accounts, the Jabber Zeus crew would modify the firm’s payroll to add dozens of “money mules,” people recruited through elaborate work-at-home schemes to handle bank transfers. The mules in turn would forward any stolen payroll deposits — minus their commissions — via wire transfers to other mules in Ukraine and the United Kingdom.

The 2012 indictment targeting the Jabber Zeus crew named MrICQ as “John Doe #3,” and said this person handled incoming notifications of newly compromised victims. The Department of Justice (DOJ) said MrICQ also helped the group launder the proceeds of their heists through electronic currency exchange services.

Two sources familiar with the Jabber Zeus investigation said Rybtsov was arrested in Italy, although the exact date and circumstances of his arrest remain unclear. A summary of recent decisions (PDF) published by the Italian Supreme Court states that in April 2025, Rybtsov lost a final appeal to avoid extradition to the United States.

According to the mugshot website lockedup[.]wtf, Rybtsov arrived in Nebraska on October 9, and was being held under an arrest warrant from the U.S. Federal Bureau of Investigation (FBI).

The data breach tracking service Constella Intelligence found breached records from the business profiling site bvdinfo[.]com showing that a 41-year-old Yuriy Igorevich Rybtsov worked in a building at 59 Barnaulska St. in Donetsk. Further searching on this address in Constella finds the same apartment building was shared by a business registered to Vyacheslav “Tank” Penchukov, the leader of the Jabber Zeus crew in Ukraine.

Penchukov was arrested in 2022 while traveling to meet his wife in Switzerland. Last year, a federal court in Nebraska sentenced Penchukov to 18 years in prison and ordered him to pay more than $73 million in restitution.

Lawrence Baldwin is founder of myNetWatchman, a threat intelligence company based in Georgia that began tracking and disrupting the Jabber Zeus gang in 2009. myNetWatchman had secretly gained access to the Jabber chat server used by the Ukrainian hackers, allowing Baldwin to eavesdrop on the daily conversations between MrICQ and other Jabber Zeus members.

Baldwin shared those real-time chat records with multiple state and federal law enforcement agencies, and with this reporter. Between 2010 and 2013, I spent several hours each day alerting small businesses across the country that their payroll accounts were about to be drained by these cybercriminals.

Those notifications, and Baldwin’s tireless efforts, saved countless would-be victims a great deal of money. In most cases, however, we were already too late. Nevertheless, the pilfered Jabber Zeus group chats provided the basis for dozens of stories published here about small businesses fighting their banks in court over six- and seven-figure financial losses.

Baldwin said the Jabber Zeus crew was far ahead of its peers in several respects. For starters, their intercepted chats showed they worked to create a highly customized botnet directly with the author of the original Zeus Trojan — Evgeniy Mikhailovich Bogachev, a Russian man who has long been on the FBI’s “Most Wanted” list. The feds have a standing $3 million reward for information leading to Bogachev’s arrest.

The core innovation of Jabber Zeus was an alert that MrICQ would receive each time a new victim entered a one-time password code into a phishing page mimicking their financial institution. The gang’s internal name for this component was “Leprechaun,” (the video below from myNetWatchman shows it in action). Jabber Zeus would actually re-write the HTML code as displayed in the victim’s browser, allowing them to intercept any passcodes sent by the victim’s bank for multi-factor authentication.

“These guys had compromised such a large number of victims that they were getting buried in a tsunami of stolen banking credentials,” Baldwin told KrebsOnSecurity. “But the whole point of Leprechaun was to isolate the highest-value credentials — the commercial bank accounts with two-factor authentication turned on. They knew these were far juicier targets because they clearly had a lot more money to protect.”

Baldwin said the Jabber Zeus trojan also included a custom “backconnect” component that allowed the hackers to relay their pilfering of commercial bank accounts through the victim’s own infected PC.

“The Jabber Zeus crew were literally connecting to the victim’s bank account from the victim’s IP address, or from the remote control function and by fully emulating the device,” he said. “That trojan was like a hot knife through butter of what everyone thought was state-of-the-art secure online banking at the time.”

Although the Jabber Zeus crew was in direct contact with the Zeus author, the chats intercepted by myNetWatchman show Bogachev frequently ignored the group’s pleas for help. The government says the real leader of the Jabber Zeus crew was Maksim Yakubets, a 38-year Ukrainian man with Russian citizenship who went by the hacker handle “Aqua.”

The Jabber chats intercepted by Baldwin show that Aqua interacted almost daily with MrICQ, Tank and other members of the hacking team, often facilitating the group’s money mule and cashout activities remotely from Russia.

The government says Yakubets/Aqua would later emerge as the leader of an elite cybercrime ring of at least 17 hackers that referred to themselves internally as “Evil Corp.” Members of Evil Corp developed and used the Dridex (a.k.a. Bugat) trojan, which helped them siphon more than $100 million from hundreds of victim companies in the United States and Europe.

This 2019 story about the government’s $5 million bounty for information leading to Yakubets’s arrest includes excerpts of conversations between Aqua, Tank, Bogachev and other Jabber Zeus crew members discussing stories I’d written about their victims. Both Baldwin and I were interviewed at length for a new weekly six-part podcast by the BBC that delves deep into the history of Evil Corp. Episode One focuses on the evolution of Zeus, while the second episode centers on an investigation into the group by former FBI agent Jim Craig.

Aisuru, the botnet responsible for a series of record-smashing distributed denial-of-service (DDoS) attacks this year, recently was overhauled to support a more low-key, lucrative and sustainable business: Renting hundreds of thousands of infected Internet of Things (IoT) devices to proxy services that help cybercriminals anonymize their traffic. Experts says a glut of proxies from Aisuru and other sources is fueling large-scale data harvesting efforts tied to various artificial intelligence (AI) projects, helping content scrapers evade detection by routing their traffic through residential connections that appear to be regular Internet users.

First identified in August 2024, Aisuru has spread to at least 700,000 IoT systems, such as poorly secured Internet routers and security cameras. Aisuru’s overlords have used their massive botnet to clobber targets with headline-grabbing DDoS attacks, flooding targeted hosts with blasts of junk requests from all infected systems simultaneously.

In June, Aisuru hit KrebsOnSecurity.com with a DDoS clocking at 6.3 terabits per second — the biggest attack that Google had ever mitigated at the time. In the weeks and months that followed, Aisuru’s operators demonstrated DDoS capabilities of nearly 30 terabits of data per second — well beyond the attack mitigation capabilities of most Internet destinations.

These digital sieges have been particularly disruptive this year for U.S.-based Internet service providers (ISPs), in part because Aisuru recently succeeded in taking over a large number of IoT devices in the United States. And when Aisuru launches attacks, the volume of outgoing traffic from infected systems on these ISPs is often so high that it can disrupt or degrade Internet service for adjacent (non-botted) customers of the ISPs.

“Multiple broadband access network operators have experienced significant operational impact due to outbound DDoS attacks in excess of 1.5Tb/sec launched from Aisuru botnet nodes residing on end-customer premises,” wrote Roland Dobbins, principal engineer at Netscout, in a recent executive summary on Aisuru. “Outbound/crossbound attack traffic exceeding 1Tb/sec from compromised customer premise equipment (CPE) devices has caused significant disruption to wireline and wireless broadband access networks. High-throughput attacks have caused chassis-based router line card failures.”

The incessant attacks from Aisuru have caught the attention of federal authorities in the United States and Europe (many of Aisuru’s victims are customers of ISPs and hosting providers based in Europe). Quite recently, some of the world’s largest ISPs have started informally sharing block lists identifying the rapidly shifting locations of the servers that the attackers use to control the activities of the botnet.

Experts say the Aisuru botmasters recently updated their malware so that compromised devices can more easily be rented to so-called “residential proxy” providers. These proxy services allow paying customers to route their Internet communications through someone else’s device, providing anonymity and the ability to appear as a regular Internet user in almost any major city worldwide.

From a website’s perspective, the IP traffic of a residential proxy network user appears to originate from the rented residential IP address, not from the proxy service customer. Proxy services can be used in a legitimate manner for several business purposes — such as price comparisons or sales intelligence. But they are massively abused for hiding cybercrime activity (think advertising fraud, credential stuffing) because they can make it difficult to trace malicious traffic to its original source.

And as we’ll see in a moment, this entire shadowy industry appears to be shifting its focus toward enabling aggressive content scraping activity that continuously feeds raw data into large language models (LLMs) built to support various AI projects.

‘INSANE’ GROWTH

Riley Kilmer is co-founder of spur.us, a service that tracks proxy networks. Kilmer said all of the top proxy services have grown exponentially over the past six months — with some adding between 10 to 200 times more proxies for rent.

“I just checked, and in the last 90 days we’ve seen 250 million unique residential proxy IPs,” Kilmer said. “That is insane. That is so high of a number, it’s unheard of. These proxies are absolutely everywhere now.”

To put Kilmer’s comments in perspective, here was Spur’s view of the Top 10 proxy networks by approximate install base, circa May 2025:

AUPROXIES_PROXY  66,097
RAYOBYTE_PROXY    43,894
OXYLABS_PROXY   43,008
WEBSHARE_PROXY   39,800
IPROYAL_PROXY    32,723
PROXYCHEAP_PROXY    26,368
IPIDEA_PROXY    26,202
MYPRIVATEPROXY_PROXY  25,287
HYPE_PROXY    18,185
MASSIVE_PROXY    17,152

Today, Spur says it is tracking an unprecedented spike in available proxies across all providers, including;

LUMINATI_PROXY    11,856,421
NETNUT_PROXY    10,982,458
ABCPROXY_PROXY    9,294,419
OXYLABS_PROXY     6,754,790
IPIDEA_PROXY     3,209,313
EARNFM_PROXY    2,659,913
NODEMAVEN_PROXY    2,627,851
INFATICA_PROXY    2,335,194
IPROYAL_PROXY    2,032,027
YILU_PROXY    1,549,155

Reached for comment about the apparent rapid growth in their proxy network, Oxylabs (#4 on Spur’s list) said while their proxy pool did grow recently, it did so at nowhere near the rate cited by Spur.

“We don’t systematically track other providers’ figures, and we’re not aware of any instances of 10× or 100× growth, especially when it comes to a few bigger companies that are legitimate businesses,” the company said in a written statement.

Bright Data was formerly known as Luminati Networks, the name that is currently at the top of Spur’s list of the biggest residential proxy networks, with more than 11 million proxies. Bright Data likewise told KrebsOnSecurity that Spur’s current estimates of its proxy network are dramatically overstated and inaccurate.

“We did not actively initiate nor do we see any 10x or 100x expansion of our network, which leads me to believe that someone might be presenting these IPs as Bright Data’s in some way,” said Rony Shalit, Bright Data’s chief compliance and ethics officer. “In many cases in the past, due to us being the leading data collection proxy provider, IPs were falsely tagged as being part of our network, or while being used by other proxy providers for malicious activity.”

“Our network is only sourced from verified IP providers and a robust opt-in only residential peers, which we work hard and in complete transparency to obtain,” Shalit continued. “Every DC, ISP or SDK partner is reviewed and approved, and every residential peer must actively opt in to be part of our network.”

HK NETWORK

Even Spur acknowledges that Luminati and Oxylabs are unlike most other proxy services on their top proxy providers list, in that these providers actually adhere to “know-your-customer” policies, such as requiring video calls with all customers, and strictly blocking customers from reselling access.

Benjamin Brundage is founder of Synthient, a startup that helps companies detect proxy networks. Brundage said if there is increasing confusion around which proxy networks are the most worrisome, it’s because nearly all of these lesser-known proxy services have evolved into highly incestuous bandwidth resellers. What’s more, he said, some proxy providers do not appreciate being tracked and have been known to take aggressive steps to confuse systems that scan the Internet for residential proxy nodes.

Brundage said most proxy services today have created their own software development kit or SDK that other app developers can bundle with their code to earn revenue. These SDKs quietly modify the user’s device so that some portion of their bandwidth can be used to forward traffic from proxy service customers.

“Proxy providers have pools of constantly churning IP addresses,” he said. “These IP addresses are sourced through various means, such as bandwidth-sharing apps, botnets, Android SDKs, and more. These providers will often either directly approach resellers or offer a reseller program that allows users to resell bandwidth through their platform.”

Many SDK providers say they require full consent before allowing their software to be installed on end-user devices. Still, those opt-in agreements and consent checkboxes may be little more than a formality for cybercriminals like the Aisuru botmasters, who can earn a commission each time one of their infected devices is forced to install some SDK that enables one or more of these proxy services.

Depending on its structure, a single provider may operate hundreds of different proxy pools at a time — all maintained through other means, Brundage said.

“Often, you’ll see resellers maintaining their own proxy pool in addition to an upstream provider,” he said. “It allows them to market a proxy pool to high-value clients and offer an unlimited bandwidth plan for cheap reduce their own costs.”

Some proxy providers appear to be directly in league with botmasters. Brundage identified one proxy provider that was aggressively advertising cheap and plentiful bandwidth to content scraping companies. After scanning that provider’s pool of available proxies, Brundage said he found a one-to-one match with IP addresses he’d previously mapped to the Aisuru botnet.

Brundage says that by almost any measurement, the world’s largest residential proxy service is IPidea, a China-based proxy network. IPidea is #5 on Spur’s Top 10, and Brundage said its brands include ABCProxy (#3), Roxlabs, LunaProxy, PIA S5 Proxy, PyProxy, 922Proxy, 360Proxy, IP2World, and Cherry Proxy. Spur’s Kilmer said they also track Yilu Proxy (#10) as IPidea.

Brundage said all of these providers operate under a corporate umbrella known on the cybercrime forums as “HK Network.”

“The way it works is there’s this whole reseller ecosystem, where IPidea will be incredibly aggressive and approach all these proxy providers with the offer, ‘Hey, if you guys buy bandwidth from us, we’ll give you these amazing reseller prices,'” Brundage explained. “But they’re also very aggressive in recruiting resellers for their apps.”

Those apps include a range of low-cost and “free” virtual private networking (VPN) services that indeed allow users to enjoy a free VPN, but which also turn the user’s device into a traffic relay that can be rented to cybercriminals, or else parceled out to countless other proxy networks.

“They have all this bandwidth to offload,” Brundage said of IPidea and its sister networks. “And they can do it through their own platforms, or they go get resellers to do it for them by advertising on sketchy hacker forums to reach more people.”

One of IPidea’s core brands is 922S5Proxy, which is a not-so-subtle nod to the 911S5Proxy service that was hugely popular between 2015 and 2022. In July 2022, KrebsOnSecurity published a deep dive into 911S5Proxy’s origins and apparent owners in China. Less than a week later, 911S5Proxy announced it was closing down after the company’s servers were massively hacked.

That 2022 story named Yunhe Wang from Beijing as the apparent owner and/or manager of the 911S5 proxy service. In May 2024, the U.S. Department of Justice arrested Mr Wang, alleging that his network was used to steal billions of dollars from financial institutions, credit card issuers, and federal lending programs. At the same time, the U.S. Treasury Department announced sanctions against Wang and two other Chinese nationals for operating 911S5Proxy.

DATA SCRAPING FOR AI

In recent months, multiple experts who track botnet and proxy activity have shared that a great deal of content scraping which ultimate benefits AI companies is now leveraging these proxy networks to further obfuscate their aggressive data-slurping activity. That’s because by routing it through residential IP addresses, content scraping firms can make their traffic far trickier to filter out.

“It’s really difficult to block, because there’s a risk of blocking real people,” Spur’s Kilmer said of the LLM scraping activity that is fed through individual residential IP addresses, which are often shared by multiple customers at once.

Kilmer says the AI industry has brought a veneer of legitimacy to residential proxy business, which has heretofore mostly been associated with sketchy affiliate money making programs, automated abuse, and unwanted Internet traffic.

“Web crawling and scraping has always been a thing, but AI made it like a commodity, data that had to be collected,” Kilmer said. “Everybody wanted to monetize their own data pots, and how they monetize that is different across the board.”

Kilmer said many LLM-related scrapers rely on residential proxies in cases where the content provider has restricted access to their platform in some way, such as forcing interaction through an app, or keeping all content behind a login page with multi-factor authentication.

“Where the cost of data is out of reach — there is some exclusivity or reason they can’t access the data — they’ll turn to residential proxies so they look like a real person accessing that data,” Kilmer said of the content scraping efforts.

Aggressive AI crawlers increasingly are overloading community-maintained infrastructure, causing what amounts to persistent DDoS attacks on vital public resources. A report earlier this year from LibreNews found some open-source projects now see as much as 97 percent of their traffic originating from AI company bots, dramatically increasing bandwidth costs, service instability, and burdening already stretched-thin maintainers.

Cloudflare is now experimenting with tools that will allow content creators to charge a fee to AI crawlers to scrape their websites. The company’s “pay-per-crawl” feature is currently in a private beta, but it lets publishers set their own prices that bots must pay before scraping content.

On October 22, the social media and news network Reddit sued Oxylabs (PDF) and several other proxy providers, alleging that their systems enabled the mass-scraping of Reddit user content even though Reddit had taken steps to block such activity.

“Recognizing that Reddit denies scrapers like them access to its site, Defendants scrape the data from Google’s search results instead,” the lawsuit alleges. “They do so by masking their identities, hiding their locations, and disguising their web scrapers as regular people (among other techniques) to circumvent or bypass the security restrictions meant to stop them.”

Denas Grybauskas, chief governance and strategy officer at Oxylabs, said the company was shocked and disappointed by the lawsuit.

“Reddit has made no attempt to speak with us directly or communicate any potential concerns,” Grybauskas said in a written statement. “Oxylabs has always been and will continue to be a pioneer and an industry leader in public data collection, and it will not hesitate to defend itself against these allegations. Oxylabs’ position is that no company should claim ownership of public data that does not belong to them. It is possible that it is just an attempt to sell the same public data at an inflated price.”

As big and powerful as Aisuru may be, it is hardly the only botnet that is contributing to the overall broad availability of residential proxies. For example, on June 5 the FBI’s Internet Crime Complaint Center warned that an IoT malware threat dubbed BADBOX 2.0 had compromised millions of smart-TV boxes, digital projectors, vehicle infotainment units, picture frames, and other IoT devices.

In July 2025, Google filed a lawsuit in New York federal court against the Badbox botnet’s alleged perpetrators. Google said the Badbox 2.0 botnet “compromised more than 10 million uncertified devices running Android’s open-source software, which lacks Google’s security protections. Cybercriminals infected these devices with pre-installed malware and exploited them to conduct large-scale ad fraud and other digital crimes.”

A FAMILIAR DOMAIN NAME

Brundage said the Aisuru botmasters have their own SDK, and for some reason part of its code tells many newly-infected systems to query the domain name fuckbriankrebs[.]com. This may be little more than an elaborate “screw you” to this site’s author: One of the botnet’s alleged partners goes by the handle “Forky,” and was identified in June by KrebsOnSecurity as a young man from Sao Paulo, Brazil.

Brundage noted that only systems infected with Aisuru’s Android SDK will be forced to resolve the domain. Initially, there was some discussion about whether the domain might have some utility as a “kill switch” capable of disrupting the botnet’s operations, although Brundage and others interviewed for this story say that is unlikely.

For one thing, they said, if the domain was somehow critical to the operation of the botnet, why was it still unregistered and actively for-sale? Why indeed, we asked. Happily, the domain name was deftly snatched up last week by Philippe Caturegli, “chief hacking officer” for the security intelligence company Seralys.

Caturegli enabled a passive DNS server on that domain and within a few hours received more than 700,000 requests for unique subdomains on fuckbriankrebs[.]com.

But even with that visibility into Aisuru, it is difficult to use this domain check-in feature to measure its true size, Brundage said. After all, he said, the systems that are phoning home to the domain are only a small portion of the overall botnet.

“The bots are hardcoded to just spam lookups on the subdomains,” he said. “So anytime an infection occurs or it runs in the background, it will do one of those DNS queries.”

The domain fuckbriankrebs[.]com has a storied history. On its initial launch in 2009, it was used to spread malicious software by the Cutwail spam botnet. In 2011, the domain was involved in a notable DDoS against this website from a botnet powered by Russkill (a.k.a. “Dirt Jumper”).

Domaintools.com finds that in 2015, fuckbriankrebs[.]com was registered to an email address attributed to David “Abdilo” Crees, a 26-year-old Australian man sentenced in May 2025 to time served for cybercrime convictions related to the Lizard Squad hacking group.

Financial regulators in Canada this week levied $176 million in fines against Cryptomus, a digital payments platform that supports dozens of Russian cryptocurrency exchanges and websites hawking cybercrime services. The penalties for violating Canada’s anti money-laundering laws come ten months after KrebsOnSecurity noted that Cryptomus’s Vancouver street address was home to dozens of foreign currency dealers, money transfer businesses, and cryptocurrency exchanges — none of which were physically located there.

On October 16, the Financial Transactions and Reports Analysis Center of Canada (FINTRAC) imposed a $176,960,190 penalty on Xeltox Enterprises Ltd., more commonly known as the cryptocurrency payments platform Cryptomus.

FINTRAC found that Cryptomus failed to submit suspicious transaction reports in cases where there were reasonable grounds to suspect that they were related to the laundering of proceeds connected to trafficking in child sexual abuse material, fraud, ransomware payments and sanctions evasion.

“Given that numerous violations in this case were connected to trafficking in child sexual abuse material, fraud, ransomware payments and sanctions evasion, FINTRAC was compelled to take this unprecedented enforcement action,” said Sarah Paquet, director and CEO at the regulatory agency.

In December 2024, KrebsOnSecurity covered research by blockchain analyst and investigator Richard Sanders, who’d spent several months signing up for various cybercrime services, and then tracking where their customer funds go from there. The 122 services targeted in Sanders’s research all used Cryptomus, and included some of the more prominent businesses advertising on the cybercrime forums, such as:

-abuse-friendly or “bulletproof” hosting providers like anonvm[.]wtf, and PQHosting;
-sites selling aged email, financial, or social media accounts, such as verif[.]work and kopeechka[.]store;
-anonymity or “proxy” providers like crazyrdp[.]com and rdp[.]monster;
-anonymous SMS services, including anonsim[.]net and smsboss[.]pro.

Sanders found at least 56 cryptocurrency exchanges were using Cryptomus to process transactions, including financial entities with names like casher[.]su, grumbot[.]com, flymoney[.]biz, obama[.]ru and swop[.]is.

“These platforms were built for Russian speakers, and they each advertised the ability to anonymously swap one form of cryptocurrency for another,” the December 2024 story noted. “They also allowed the exchange of cryptocurrency for cash in accounts at some of Russia’s largest banks — nearly all of which are currently sanctioned by the United States and other western nations.”

Reached for comment on FINTRAC’s action, Sanders told KrebsOnSecurity he was surprised it took them so long.

“I have no idea why they don’t just sanction them or prosecute them,” Sanders said. “I’m not let down with the fine amount but it’s also just going to be the cost of doing business to them.”

The $173 million fine is a significant sum for FINTRAC, which imposed 23 such penalties last year totaling less than $26 million. But Sanders says FINTRAC still has much work to do in pursuing other shadowy money service businesses (MSBs) that are registered in Canada but are likely money laundering fronts for entities based in Russia and Iran.

In an investigation published in July 2024, CTV National News and the Investigative Journalism Foundation (IJF) documented dozens of cases across Canada where multiple MSBs are incorporated at the same address, often without the knowledge or consent of the location’s actual occupant.

Their inquiry found that the street address for Cryptomus parent Xeltox Enterprises was listed as the home of at least 76 foreign currency dealers, eight MSBs, and six cryptocurrency exchanges. At that address is a three-story building that used to be a bank and now houses a massage therapy clinic and a co-working space. But the news outlets found none of the MSBs or currency dealers were paying for services at that co-working space.

The reporters also found another collection of 97 MSBs clustered at an address for a commercial office suite in Ontario, even though there was no evidence any of these companies had ever arranged for any business services at that address.

Cybercriminals are abusing a widespread lack of authentication in the customer service platform Zendesk to flood targeted email inboxes with menacing messages that come from hundreds of Zendesk corporate customers simultaneously.

Zendesk is an automated help desk service designed to make it simple for people to contact companies for customer support issues. Earlier this week, KrebsOnSecurity started receiving thousands of ticket creation notification messages through Zendesk in rapid succession, each bearing the name of different Zendesk customers, such as CapCom, CompTIA, Discord, GMAC, NordVPN, The Washington Post, and Tinder.

The abusive missives sent via Zendesk’s platform can include any subject line chosen by the abusers. In my case, the messages variously warned about a supposed law enforcement investigation involving KrebsOnSecurity.com, or else contained personal insults.

Moreover, the automated messages that are sent out from this type of abuse all come from customer domain names — not from Zendesk. In the example below, replying to any of the junk customer support responses from The Washington Post’s Zendesk installation shows the reply-to address is help@washpost.com.

Notified about the mass abuse of their platform, Zendesk said the emails were ticket creation notifications from customer accounts that configured their Zendesk instance to allow anyone to submit support requests — including anonymous users.

“These types of support tickets can be part of a customer’s workflow, where a prior verification is not required to allow them to engage and make use of the Support capabilities,” said Carolyn Camoens, communications director at Zendesk. “Although we recommend our customers to permit only verified users to submit tickets, some Zendesk customers prefer to use an anonymous environment to allow for tickets to be created due to various business reasons.”

Camoens said requests that can be submitted in an anonymous manner can also make use of an email address of the submitter’s choice.

“However, this method can also be used for spam requests to be created on behalf of third party email addresses,” Camoens said. “If an account has enabled the auto-responder trigger based on ticket creation, then this allows for the ticket notification email to be sent from our customer’s accounts to these third parties. The notification will also include the Subject added by the creator of these tickets.”

Zendesk claims it uses rate limits to prevent a high volume of requests from being created at once, but those limits did not stop Zendesk customers from flooding my inbox with thousands of messages in just a few hours.

“We recognize that our systems were leveraged against you in a distributed, many-against-one manner,” Camoens said. “We are actively investigating additional preventive measures. We are also advising customers experiencing this type of activity to follow our general security best practices and configure an authenticated ticket creation workflow.”

In all of the cases above, the messaging abuse would not have been possible if Zendesk customers validated support request email addresses prior to sending responses. Failing to do so may make it easier for Zendesk clients to handle customer support requests, but it also allows ne’er-do-wells to sully the sender’s brand in service of disruptive and malicious email floods.

Microsoft today released software updates to plug a whopping 172 security holes in its Windows operating systems, including at least two vulnerabilities that are already being actively exploited. October’s Patch Tuesday also marks the final month that Microsoft will ship security updates for Windows 10 systems. If you’re running a Windows 10 PC and you’re unable or unwilling to migrate to Windows 11, read on for other options.

The first zero-day bug addressed this month (CVE-2025-24990) involves a third-party modem driver called Agere Modem that’s been bundled with Windows for the past two decades. Microsoft responded to active attacks on this flaw by completely removing the vulnerable driver from Windows.

The other zero-day is CVE-2025-59230, an elevation of privilege vulnerability in Windows Remote Access Connection Manager (also known as RasMan), a service used to manage remote network connections through virtual private networks (VPNs) and dial-up networks.

“While RasMan is a frequent flyer on Patch Tuesday, appearing more than 20 times since January 2022, this is the first time we’ve seen it exploited in the wild as a zero day,” said Satnam Narang, senior staff research engineer at Tenable.

Narang notes that Microsoft Office users should also take note of CVE-2025-59227 and CVE-2025-59234, a pair of remote code execution bugs that take advantage of “Preview Pane,” meaning that the target doesn’t even need to open the file for exploitation to occur. To execute these flaws, an attacker would social engineer a target into previewing an email with a malicious Microsoft Office document.

Speaking of Office, Microsoft quietly announced this week that Microsoft Word will now automatically save documents to OneDrive, Microsoft’s cloud platform. Users who are uncomfortable saving all of their documents to Microsoft’s cloud can change this in Word’s settings; ZDNet has a useful how-to on disabling this feature.

Kev Breen, senior director of threat research at Immersive, called attention to CVE-2025-59287, a critical remote code execution bug in the Windows Server Update Service  (WSUS) — the very same Windows service responsible for downloading security patches for Windows Server versions. Microsoft says there are no signs this weakness is being exploited yet. But with a threat score of 9.8 out of possible 10 and marked “exploitation more likely,” CVE-2025-59287 can be exploited without authentication and is an easy “patch now” candidate.

“Microsoft provides limited information, stating that an unauthenticated attacker with network access can send untrusted data to the WSUS server, resulting in deserialization and code execution,” Breen wrote. “As WSUS is a trusted Windows service that is designed to update privileged files across the file system, an attacker would have free rein over the operating system and could potentially bypass some EDR detections that ignore or exclude the WSUS service.”

For more on other fixes from Redmond today, check out the SANS Internet Storm Center monthly roundup, which indexes all of the updates by severity and urgency.

Windows 10 isn’t the only Microsoft OS that is reaching end-of-life today; Exchange Server 2016, Exchange Server 2019, Skype for Business 2016, Windows 11 IoT Enterprise Version 22H2, and Outlook 2016 are some of the other products that Microsoft is sunsetting today.

If you’re running any Windows 10 systems, you’ve probably already determined whether your PC meets the technical hardware specs recommended for the Windows 11 OS. If you’re reluctant or unable to migrate a Windows 10 system to Windows 11, there are alternatives to simply continuing to use Windows 10 without ongoing security updates.

One option is to pay for another year’s worth of security updates through Microsoft’s Extended Security Updates (ESU) program. The cost is just $30 if you don’t have a Microsoft account, and apparently free if you register the PC to a Microsoft account. This video breakdown from Ask Your Computer Guy does a good job of walking Windows 10 users through this process. Microsoft emphasizes that ESU enrollment does not provide other types of fixes, feature improvements or product enhancements. It also does not come with technical support.

Windows 10 users also have the option of installing some flavor of Linux instead. Anyone seriously considering this option should check out the website endof10.org, which includes a plethora of tips and a DIY installation guide.

Linux Mint is a great option for Linux newbies. Like most modern Linux versions, Mint will run on anything with a 64-bit CPU that has at least 2GB of memory, although 4GB is recommended. In other words, it will run on almost any computer produced in the last decade.

Linux Mint also is likely to be the most intuitive interface for regular Windows users, and it is largely configurable without any fuss at the text-only command-line prompt. Mint and other flavors of Linux come with LibreOffice, which is an open source suite of tools that includes applications similar to Microsoft Office, and it can open, edit and save documents as Microsoft Office files.

If you’d prefer to give Linux a test drive before installing it on a Windows PC, you can always just download it to a removable USB drive. From there, reboot the computer (with the removable drive plugged in) and select the option at startup to run the operating system from the external USB drive. If you don’t see an option for that after restarting, try restarting again and hitting the F8 button, which should open a list of bootable drives. Here’s a fairly thorough tutorial that walks through exactly how to do all this.

And if this is your first time trying out Linux, relax and have fun: The nice thing about a “live” version of Linux (as it’s called when the operating system is run from a removable drive such as a CD or a USB stick) is that none of your changes persist after a reboot. Even if you somehow manage to break something, a restart will return the system back to its original state.

As ever, if you experience any difficulties during or after applying this month’s batch of patches, please leave a note about it in the comments below.