Authorities in Santa Clara, Calif. have arrested and charged a 19-year-old area man on suspicion hijacking mobile phone numbers as part of a scheme to steal large sums of bitcoin and other cryptocurrencies. The arrest is the third known law enforcement action this month targeting “SIM swappers,” individuals who specialize in stealing wireless phone numbers and hijacking online financial and social media accounts tied to those numbers.

Xzavyer Clemente Narvaez was arrested Aug. 17, 2018 by investigators working with Santa Clara County’s “REACT task force,” which says it’s targeting those involved in “the takeovers of cell phone, email and financial accounts resulting in the theft of cryptocurrency.”

Prosecutors allege Narvaez used the proceeds of his crimes (estimated at > $1 million in virtual currencies) to purchase luxury items, including a McLaren — a $200,000 high-performance sports car. Investigators said they interviewed several alleged victims of Narvaez, including one man who reported being robbed of $150,000 in virtual currencies after his phone number was hijacked.

A fraudulent SIM swap occurs when a victim’s cell phone service is redirected from a SIM card under the control of the victim to one under the control of the suspect, without the knowledge or authorization of the victim account holder.

When a victim experiences a fraudulent SIM swap, their phone suddenly has no service and all incoming calls and text messages are sent to the attacker’s device. This includes any one-time codes sent via text message or automated phone call that many companies use to supplement passwords for their online accounts.

Narvaez came to law enforcement’s attention following the arrest of Joel Ortiz, a gifted 20-year-old college student from Boston who was charged in July 2018 with using SIM swaps to steal more than $5 million in cryptocurrencies from 40 victims.

A redacted statement of facts Santa Clara prosecutors shared with KrebsOnSecurity says records obtained from Google revealed that a cellular device used by Ortiz to commit SIM swaps had at one point been used to access the Google account identified as Xzavyer.Narvaez@gmail.com.

That statement refers frequently to the term IMEI; this is the International Mobile Equipment Identity number, which is a unique identification number or serial number that all mobile phones and smartphones have.

Prosecutors used data gathered from a large number of tech companies to put Narvaez’s phone in specific places near his home in Tracy, Calif. at the time his alleged victims reported having their phones hijacked. His alleged re-use of the same mobile device for multiple SIM hijacks ultimately gave him away:

“On 7/18/18, investigators received information from an AT&T investigator regarding unauthorized SIM swaps conducted through an AT&T authorized retailer. He reported that approximately 28 SIM swaps were conducted using the same employee ID number over an approximately two-week time period in November 2017. Records were obtained that included a list of IMEI numbers used to take over the victims’ cell phone numbers.”

“AT&T provided call detail records pertaining to the IMEI numbers listed to conduct the SIM swaps. One of those IMEI numbers, ending in 3218, was used to take over the cell phone of a resident of Illinois. I contacted the victim who verified that some of his accounts had been “hacked” in late 2017 but said he did not suffer any financial loss. Sgt. Tarazi analyzed the AT&T location data pertaining to that account takeover. That data indicated that on 7/27/17, when the victim from Illinois lost access to his accounts, the IMEI (ending in 3218) of the cell phone controlling the victim’s cell phone number was located in Tracy, California.”

“The specific tower is located approximately 0.6 miles away from the address 360 Yosemite Drive in Tracy. Several “NELOS” records (GPS coordinates logged by AT&T to estimate the location of devices on their network) indicate the phone was within 1000 meters of 360 Yosemite Drive in Tracy. AT&T also provided call detail records pertaining to Narvaez’ cell phone account, which was linked to him through financial services account records. Sgt. Tarazi examined those records and determined that Narvaez’ own cell phone was connected to the same tower and sector during approximately the same time frame that the suspect device (ending in 3218) was connected to the victim’s account.”

Apple responded to requests with records pertaining to customer accounts linked to that same suspect IMEI number. Those records identified three California residents whose Apple accounts were linked to that same IMEI number.

Verizon provided call detail records pertaining to the IMEI number ending in 3218. From the statement of facts:

These records that this phone had in fact been used to access the two Verizon numbers listed above, and at the same time was connected to a Verizon celltower located approximately 1.3 miles away from 360 Yosemite Drive in Tracy, CA. This cell tower was the closest Verizon tower to 360 Yosemite Drive.

“Records obtained from DMV indicated the 2018 McLaren was purchased from a car dealership in Southern California. Sale records obtained from the dealership indicated the payment for the vehicle was made by Tiffany Ross, primarily using bitcoin, accepted by the merchant processor BitPay on behalf of the dealership. The remainder of the price of the vehicle was financed through the trade-in of a 2012 Audi R8. The buyer/s listed email address was a Gmail address. Records also indicated the Audi R8 had been purchased in June 2017 by Xzavyer Narvaez. The entire balance for that vehicle was paid using bitcoin.”

“A different Gmail address was listed under the buyer’s contact information. Google provided records indicating both e-mail addresses used to pay for the vehicles belonged to Xzavyer Narvaez.”

“BitPay provided records that identified the Bitcoin transactions in which the vehicles were purchased. Investigator Berry utilized the Bitcoin blockchain, which is the distributed public ledger of all historical transactions on the Bitcoin network, to trace the flow of the bitcoins used to purchase the McLaren back to an address attributed to the cryptocurrency exchanger Bittrex.”

“Bittrex verified that funds from Bittrex to the output address identified in the blockchain that led to the purchase of the McLaren came from Narvaez’ account, and verified the address utilized for the deposit of bitcoin into that account. The Bitcoin blockchain currently indicates that Narvaez’ Bittrex deposit address has had more than 157 bitcoin flow through it, in 208 transactions, between 7/12/18 and 3/12/18. Based on the current market value of a bitcoin, 157 bitcoins are currently worth approximately S1,000,000.”

Narvaez faces four counts of using personal identifying information without authorization; four counts of altering and damaging computer data with intent to defraud or obtain money, or other value; and grand theft of personal property of a value over nine hundred and fifty thousand dollars. He is expected to issue a plea on Sept. 26, 2018. A copy of the charges against him is here (PDF).

Federal authorities also have been active in targeting SIM swappers of late. One day after Narvaez was apprehended, police in Florida arrested a 25-year-old man accused of being part of a group of about nine people that allegedly stole hundreds of thousands of dollars in virtual currencies from SIM swap victims. That case drew on collaboration with Homeland Security Investigations, which acted on a tip from a concerned mom in Michigan who overheard her son impersonating an AT&T employee and found bags of SIM cards in his room.

All of the major wireless companies let customers protect their accounts from SIM swapping by selecting a personal identification number (PIN) that is supposed to be required when account changes are requested in person or over the phone. But one big part of the problem is that many of these SIM swappers are working directly with retail mobile store employees who know how to bypass these protections.

If you’re concerned about the threat from SIM hijacking, experts say it might be time to disconnect your mobile phone number from important accounts. We discussed options for doing just that in last week’s column, Hanging Up on Mobile in the Name of Security.

On Sunday, Aug. 12, KrebsOnSecurity carried an exclusive: The FBI was warning banks about an imminent “ATM cashout” scheme about to unfold across the globe, thanks to a data breach at an unknown financial institution. On Aug. 14, a bank in India disclosed hackers had broken into its servers, stealing nearly $2 million in fraudulent bank transfers and $11.5 million unauthorized ATM withdrawals from more than two dozen cash machines across multiple countries.

The FBI put out its alert on Friday, Aug. 10. The criminals who hacked into Pune, India-based Cosmos Bank executed their two-pronged heist the following day, sending co-conspirators to fan out and withdraw a total of about $11.5 million from 25 ATMs in Canada, Hong Kong and India.

The FBI warned it had intelligence indicating that criminals had breached an unknown payment provider’s network with malware to access bank customer card information and exploit network access, enabling large scale theft of funds from ATMs.

Organized cybercrime gangs that coordinate these so-called “unlimited attacks” typically do so by hacking or phishing their way into a bank or payment card processor. Just prior to executing on ATM cashouts, the intruders will remove many fraud controls at the financial institution, such as maximum withdrawal amounts and any limits on the number of customer ATM transactions daily.

The perpetrators alter account balances and security measures to make an unlimited amount of money available at the time of the transactions, allowing for large amounts of cash to be quickly removed from the ATM.

My story about the FBI alert was breaking news on Sunday, but it was just a day short of useful to financial institutions impacted by the breach and associated ATM cashout blitz.

But according to Indian news outlet Dailypionneer.com, there was a second attack carried out on August 13, when the Cosmos Bank hackers transferred nearly $2 million to the account of ALM Trading Limited at Hang Seng Bank in Hong Kong.

“The bank came to know about the malware attack on its debit card payment system on August 11, when it was observed that unusually repeated transactions were taking place through ATM VISA and Rupay Card for nearly two hours,” writes TN Raghunatha for the Daily Pioneer.

Cosmos Bank was quick to point out that the attackers did not access systems tied to customer accounts, and that the money taken was from the bank’s operating accounts. The 112-year-old bank blamed the attack on “a switch which is operative for the payment gateway of VISA/Rupay Debit card and not on the core banking system of the bank, the customers’ accounts and the balances are not at all affected.”

Visa issued a statement saying it was aware of the compromise affecting a client financial institution in India.

“Our systems were able to identify the issue quickly, enabling the financial institution to take appropriate action,” the company said. “Visa is working closely with the client in supporting their ongoing investigations on the matter.”

The FBI said these types of ATM cashouts are most common at smaller financial institutions that may not have sufficient resources dedicated to staying up to date with the latest security measures for handling payment card data.

“Historic compromises have included small-to-medium size financial institutions, likely due to less robust implementation of cyber security controls, budgets, or third-party vendor vulnerabilities,” the alert read. “The FBI expects the ubiquity of this activity to continue or possibly increase in the near future.”

In July 2018, KrebsOnSecurity broke the news of two separate cyber break-ins at tiny National Bank of Blacksburg in Virginia in a span of just eight months that led to ATM cashouts netting thieves more than $2.4 million. The Blacksburg bank is now suing its insurance provider for refusing to fully cover the loss.

As reported by Reuters, Cosmos Bank said in a press statement that its main banking software receives debit card payment requests via a “switching system” that was bypassed in the attack. “During the malware attack, a proxy switch was created and all the fraudulent payment approvals were passed by the proxy switching system,” the bank said.

Translation: If a financial institution is not fully encrypting its payment processing network, this can allow intruders with access to the network to divert and/or alter the response that gets sent when an ATM transaction is requested. In one such scenario, the network might say a given transaction should be declined, but thieves could still switch the signal for that ATM transaction from “declined” to “approved.”

One final note: Several news outlets have confused the attack that hit Cosmos Bank with another ATM crime called “jackpotting,” which requires thieves to have physical access to the inside of the cash machine and the ability to install malicious software that makes the ATM spit out large chunks of cash at once. Like ATM cashouts/unlimited operations, jackpotting attacks do not directly affect customer accounts but instead drain ATMs of currency.

An entrepreneur and virtual currency investor is suing AT&T for $224 million, claiming the wireless provider was negligent when it failed to prevent thieves from hijacking his mobile account and stealing millions of dollars in cryptocurrencies. Increasingly frequent, high-profile attacks like these are prompting some experts to say the surest way to safeguard one’s online accounts may be to disconnect them from the mobile providers entirely.

The claims come in a lawsuit filed this week in Los Angeles on behalf of Michael Terpin, who co-founded the first angel investor group for bitcoin enthusiasts in 2013. Terpin alleges that crooks stole almost $24 million worth of cryptocurrency after fraudulently executing a “SIM swap” on his mobile phone account at AT&T in early 2018.

A SIM card is the tiny, removable chip in a mobile device that allows it to connect to the provider’s network. Customers can legitimately request a SIM swap when their existing SIM card has been damaged, or when they are switching to a different phone that requires a SIM card of another size.

But SIM swaps are frequently abused by scam artists who trick mobile providers into tying a target’s service to a new SIM card and mobile phone that the attackers control. Unauthorized SIM swaps often are perpetrated by fraudsters who have already stolen or phished a target’s password, as many banks and online services rely on text messages to send users a one-time code that needs to be entered in addition to a password for online authentication.

Terpin alleges that on January 7, 2018, someone requested an unauthorized SIM swap on his AT&T account, causing his phone to go dead and sending all incoming texts and phone calls to a device the attackers controlled. Armed with that access, the intruders were able to reset credentials tied to his cryptocurrency accounts and siphon nearly $24 million worth of digital currencies.

According to Terpin, this was the second time in six months someone had hacked his AT&T number. On June 11, 2017, Terpin’s phone went dead. He soon learned his AT&T password had been changed remotely after 11 attempts in AT&T stores had failed. At the time, AT&T suggested Terpin take advantage of the company’s “extra security” feature — a customer-specified six-digit PIN which is required before any account changes can be made.

Terpin claims an investigation by AT&T into the 2018 breach found that an employee at an AT&T store in Norwich, Conn. somehow executed the SIM swap on his account without having to enter his “extra security” PIN, and that AT&T knew or should have known that employees could bypass its customer security measures.

Terpin is suing AT&T for his $24 million worth of cryptocurrencies, plus $200 million in punitive damages. A copy of his complaint is here (PDF).

AT&T declined to comment on specific claims in the lawsuit, saying only in a statement that, “We dispute these allegations and look forward to presenting our case in court.”

AN ‘IDENTITY CRISIS’?

Mobile phone companies are a major weak point in authentication because so many companies have now built their entire procedure for authenticating customers on a process that involves sending a one-time code to the customer via SMS or automated phone call.

In some cases, thieves executing SIM swaps have already phished or otherwise stolen a target’s bank or email password. But many major social media platforms — such as Instagram — allow users to reset their passwords using nothing more than text-based (SMS) authentication, meaning thieves can hijack those accounts just by having control over the target’s mobile phone number.

Allison Nixon is director of security research at Flashpoint, a security company in New York City that has been closely tracking the murky underworld of communities that teach people how to hijack phone numbers assigned to customer accounts at all of the major mobile providers.

Nixon calls the current SIM-jacking craze “a major identity crisis” for cybersecurity on multiple levels.

“Phone numbers were never originally intended as an identity document, they were designed as a way to contact people,” Nixon said. “But because of all these other companies are building in security measures, a phone number has become an identity document.”

In essence, mobile phone companies have become “critical infrastructure” for security precisely because so much is riding on who controls a given mobile number. At the same time, so little is needed to undo weak security controls put in place to prevent abuse.

“The infrastructure wasn’t designed to withstand the kind of attacks happening now,” Nixon said. “The protocols need to be changed, and there are probably laws affecting the telecom companies that need to be reviewed in light of how these companies have evolved.”

Unfortunately, with the major mobile providers so closely tied to your security, there is no way you can remove the most vulnerable chunks of this infrastructure — the mobile store employees who can be paid or otherwise bamboozled into helping these attacks succeed.

No way, that is, unless you completely disconnect your mobile phone number from any sort of SMS-based authentication you currently use, and replace it with Internet-based telephone services that do not offer “helpful” customer support — such as Google Voice.

Google Voice lets users choose a phone number that gets tied to their Google account, and any calls or messages to that number will be forwarded to your mobile number. But unlike phone numbers issued by the major mobile providers, Google Voice numbers can’t be stolen unless someone also hacks your Google password — in which case you likely have much bigger problems.

With Google Voice, there is no customer service person who can be conned over the phone into helping out. There is no retail-store employee who will sell access to your SIM information for a paltry $80 payday. In this view of security, customer service becomes a customer disservice.

Mind you, this isn’t my advice. The above statement summarizes the arguments allegedly made by one of the most accomplished SIM swap thieves in the game today. On July 12, 2018, police in California arrested Joel Ortiz, a 20-year-old college student from Boston who’s accused of using SIM swaps to steal more than $5 million in cryptocurrencies from 40 victims.

Ortiz allegedly had help from a number of unnamed accomplices who collectively targeted high-profile and wealthy people in the cryptocurrency space. In one of three brazen attacks at a bitcoin conference this year, Ortiz allegedly used his SIM swapping skills to steal more than $1.5 million from a cryptocurrency entrepreneur, including nearly $1 million the victim had crowdfunded.

Ortiz reportedly was a core member of OGUsers[dot]com, a forum that’s grown wildly popular among criminals engaging in SIM swaps to steal cryptocurrency and hijack high-value social media accounts. OG is short for “original gangster,” and it refers to a type of “street cred” for possession of social media account names that are relatively short (between one and six characters). On ogusers[dot]com, Ortiz allegedly picked the username “j”. Short usernames are considered more valuable because they confer on the account holder the appearance of an early adopter on most social networks.

Discussions on the Ogusers forum indicate Ortiz allegedly is the current occupant of perhaps the most OG username on Twitter — an account represented by the number zero “0”. The alias displayed on that twitter profile is “j0”. He also apparently controls the Instagram account by the same number, as well as the Instagram account “t”, which lists its alias as “Joel.”

Shown below is a cached snippet from an Ogusers forum posting by “j” (allegedly Ortiz), advising people to remove their mobile phone number from all important multi-factor authentication options, and to replace it with something like Google Voice.

WHAT CAN YOU DO?

All four major wireless carriers — AT&T, Sprint, T-Mobile and Verizon — let customers add security against SIM swaps and related schemes by setting a PIN that needs to be provided over the phone or in person at a store before account changes should be made. But these security features can be bypassed by incompetent or corrupt mobile store employees.

Mobile store employees who can be bought or tricked into conducting SIM swaps are known as “plugs” in the Ogusers community, and without them SIM swapping schemes become much more difficult.

Last week, KrebsOnSecurity broke the news that police in Florida had arrested a 25-year-old man who’s accused of being part of a group of at least nine individuals who routinely conducted fraudulent SIM swaps on high-value targets. Investigators in that case say they have surveillance logs that show the group discussed working directly with mobile store employees to complete the phone number heists.

In May I wrote about a 27-year-old Boston man who had his three-letter Instagram account name stolen after thieves hijacked his number at T-Mobile. Much like Mr. Terpin, the victim in that case had already taken T-Mobile’s advice and placed a PIN on his account that was supposed to prevent the transfer of his mobile number. T-Mobile ultimately acknowledged that the heist had been carried out by a rogue T-Mobile store employee.

So consider establishing a Google Voice account if you don’t already have one. In setting up a new number, Google requires you to provide a number capable of receiving text messages. Once your Google Voice number is linked to your mobile, the device at the mobile number you gave to Google should notify you instantly if anyone calls or messages the Google number (this assumes your phone has a Wi-Fi or mobile connection to the Internet).

After you’ve done that, take stock of every major account you can think of, replacing your mobile phone number with your Google Voice number in every case it is listed in your profile.

Here’s where it gets tricky. If you’re all-in for taking the anti-SIM-hacking advice allegedly offered by Mr. Ortiz, once you’ve changed all of your multi-factor authentication options from your mobile number to your Google Voice number, you then have to remove that mobile number you supplied to Google from your Google Voice account. After that, you can still manage calls/messages to and from your Google Voice number using the Google Voice mobile app.

And notice what else Ortiz advises in the screen shot above to secure one’s Gmail and other Google accounts: Using a physical security key (where possible) to replace passwords. This post from a few weeks back explains what security keys are, how they can help harden your security posture, and how to use them. If Google’s own internal security processes count for anything, the company recently told this author that none of its 85,000 employees had been successfully phished for their work credentials since January 2017, when Google began requiring all employees to use physical security keys in place of one-time passwords sent to a mobile device.

Standard disclaimer: If the only two-factor authentication offered by a company you use is based on sending a one-time code via SMS or automated phone call, this is still better than relying on simply a password alone. But one-time codes generated by a mobile phone app such as Authy or Google Authenticator are more secure than SMS-based options because they are not directly vulnerable to SIM-swapping attacks.

The web site twofactorauth.org breaks down online service providers by the types of secondary authentication offered (SMS, call, app-based one-time codes, security keys). Take a moment soon to review this important resource and harden your security posture wherever possible.

Adobe and Microsoft each released security updates for their software on Tuesday. Adobe plugged five security holes in its Flash Player browser plugin. Microsoft pushed 17 updates to fix at least 60 vulnerabilities in Windows and other software, including two “zero-day” flaws that attackers were already exploiting before Microsoft issued patches to fix them.

According to security firm Ivanti, the first of the two zero-day flaws (CVE-2018-8373) is a critical flaw in Internet Explorer that attackers could use to foist malware on IE users who browse to hacked or booby-trapped sites. The other zero-day is a bug (CVE-2018-8414) in the Windows 10 shell that could allow an attacker to run code of his choice.

Microsoft also patched more variants of the Meltdown/Spectre memory vulnerabilities, collectively dubbed “Foreshadow” by a team of researchers who discovered and reported the Intel-based flaws. For more information about how Foreshadow works, check out their academic paper (PDF), and/or the video below. Microsoft’s analysis is here.

One nifty little bug fixed in this patch batch is CVE-2018-8345. It addresses a problem in the way Windows handles shortcut files; ending in the “.lnk” extension, shortcut files are Windows components that link (hence the “lnk” extension) easy-to-recognize icons to specific executable programs, and are typically placed on the user’s Desktop or Start Menu.

That description of a shortcut file was taken verbatim from the first widely read report on what would later be dubbed the Stuxnet worm, which also employed an exploit for a weakness in the way Windows handled shortcut (.lnk) files. According to security firm Qualys, this patch should be prioritized for both workstations and servers, as the user does not need to click the file to exploit. “Simply viewing a malicious LNK file can execute code as the logged-in user,” Qualys’ Jimmy Graham wrote.

Not infrequently, Redmond ships updates that end up causing stability issues for some users, and it doesn’t hurt to wait a day or two before seeing if any major problems are reported with new updates before installing them. Microsoft doesn’t make it easy for Windows 10 users to change this setting, but it is possible. For all other Windows OS users, if you’d rather be alerted to new updates when they’re available so you can choose when to install them, there’s a setting for that in Windows Update.

It’s a good idea to get in the habit of backing up your computer before applying monthly updates from Microsoft. Windows has some built-in tools that can help recover from bad patches, but restoring the system to a backup image taken just before installing updates is often much less hassle and an added piece of mind while you’re sitting there praying for the machine to reboot successfully after patching.

Adobe’s Flash update brings the program to v. 30.0.0.154 for Windows, macOS, Chrome and Linux. Most readers here know how I feel about Flash, which is a major security liability and a frequent target of browser-based attacks. The updates from Microsoft include these Flash fixes for IE, and Google Chrome has already pushed an update to address these five Flash flaws (although a browser restart may be needed).

But seriously, if you don’t have a specific need for Flash, just disable it already. Chrome is set to ask before playing Flash objects, but disabling Flash in Chrome is simple enough. Paste “chrome://settings/content” into a Chrome browser bar and then select “Flash” from the list of items. By default it should be set to “Ask first” before running Flash, although users also can disable Flash entirely here or whitelist and blacklist specific sites.

By default, Mozilla Firefox on Windows computers with Flash installed runs Flash in a “protected mode,” which prompts the user to decide if they want to enable the plugin before Flash content runs on a Web site.

Adobe also released security updates for its PDF Reader and Acrobat products.

As always, please leave a note in the comments below if you experience any problems installing any of these updates.

The Federal Bureau of Investigation (FBI) is warning banks that cybercriminals are preparing to carry out a highly choreographed, global fraud scheme known as an “ATM cash-out,” in which crooks hack a bank or payment card processor and use cloned cards at cash machines around the world to fraudulently withdraw millions of dollars in just a few hours.

“The FBI has obtained unspecified reporting indicating cyber criminals are planning to conduct a global Automated Teller Machine (ATM) cash-out scheme in the coming days, likely associated with an unknown card issuer breach and commonly referred to as an ‘unlimited operation’,” reads a confidential alert the FBI shared with banks privately on Friday.

The FBI said unlimited operations compromise a financial institution or payment card processor with malware to access bank customer card information and exploit network access, enabling large scale theft of funds from ATMs.

“Historic compromises have included small-to-medium size financial institutions, likely due to less robust implementation of cyber security controls, budgets, or third-party vendor vulnerabilities,” the alert continues. “The FBI expects the ubiquity of this activity to continue or possibly increase in the near future.”

Organized cybercrime gangs that coordinate unlimited attacks typically do so by hacking or phishing their way into a bank or payment card processor. Just prior to executing on ATM cashouts, the intruders will remove many fraud controls at the financial institution, such as maximum ATM withdrawal amounts and any limits on the number of customer ATM transactions daily.

The perpetrators also alter account balances and security measures to make an unlimited amount of money available at the time of the transactions, allowing for large amounts of cash to be quickly removed from the ATM.

“The cyber criminals typically create fraudulent copies of legitimate cards by sending stolen card data to co-conspirators who imprint the data on reusable magnetic strip cards, such as gift cards purchased at retail stores,” the FBI warned. “At a pre-determined time, the co-conspirators withdraw account funds from ATMs using these cards.”

Virtually all ATM cashout operations are launched on weekends, often just after financial institutions begin closing for business on Saturday. Last month, KrebsOnSecurity broke a story about an apparent unlimited operation used to extract a total of $2.4 million from accounts at the National Bank of Blacksburg in two separate ATM cashouts between May 2016 and January 2017.

In both cases, the attackers managed to phish someone working at the Blacksburg, Virginia-based small bank. From there, the intruders compromised systems the bank used to manage credits and debits to customer accounts.

The 2016 unlimited operation against National Bank began Saturday, May 28, 2016 and continued through the following Monday. That particular Monday was Memorial Day, a federal holiday in the United States, meaning bank branches were closed for more than two days after the heist began. All told, the attackers managed to siphon almost $570,000 in the 2016 attack.

The Blacksburg bank hackers struck again on Saturday, January 7, and by Monday Jan 9 had succeeded in withdrawing almost $2 million in another unlimited ATM cashout operation.

The FBI is urging banks to review how they’re handling security, such as implementing strong password requirements and two-factor authentication using a physical or digital token when possible for local administrators and business critical roles.

Other tips in the FBI advisory suggested that banks:

-Implement separation of duties or dual authentication procedures for account balance or withdrawal increases above a specified threshold.

-Implement application whitelisting to block the execution of malware.

-Monitor, audit and limit administrator and business critical accounts with the authority to modify the account attributes mentioned above.

-Monitor for the presence of remote network protocols and administrative tools used to pivot back into the network and conduct post-exploitation of a network, such as Powershell, cobalt strike and TeamViewer.

-Monitor for encrypted traffic (SSL or TLS) traveling over non-standard ports.

-Monitor for network traffic to regions wherein you would not expect to see outbound connections from the financial institution.