The new ‘blue screen of death’

A technical-support phone scam which uses Ransomlock to lock the user’s computer and trick them into calling a help line is just the latest example of how cybercriminals every now and again will borrow ideas from each other.

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A fake BSoD lock screen: Source-Symantec

What’s true for businesses is also true for scams and malware, to remain successful they must evolve and adapt. Sometimes ideas or methods are borrowed from one business model and used in another to create an amalgamation. After all, some of the best creations have come about this way; out of ice-cream and yogurt was born delicious frogurt, and any reputable hunter of the undead will tell you the endless benefits of owning a sledge saw.

Cybercriminals responsible for malware and various scams also want their “businesses” to remain successful and every now and again they too borrow ideas from each other. We recently came across an example of this when we discovered a technical-support phone scam that uses a new ransomware variant (Trojan.Ransomlock.AM) that locks the user’s computer and tricks them into calling a phone number to get technical help to resolve the issue.

A game of two halves:

Ransomware

Ransomware can be divided into two main categories: Ransomware that simply locks the compromised computer’s screen (Trojan.Ransomlock), and ransomware that encrypts files found on the compromised computer (Trojan.RansomcryptTrojan.CryptowallTrojan.Cryptolocker etc.).

This year we’ve observed a major role reversal in the ransomware landscape with the cryptomalware variants overtaking the ransomlock variants in prevalence. Ransomlock variants may have lost the lead to cryptomalware variants, but they are by no means out of the game and from time-to-time we do observed newcomers that add a fresh twist to the screen-locking business model.

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Top ten ransomware detections as of 11-07-14: Source-Symantec

Technical support scams

Technical support scams are definitely not new and have been around for quite some time now. In these scams, the crooks cold call random people, often claiming to be a well-known software company, and try to convince them that their computers are full of critical errors or malware. The end goal is to get onto the victim’s computer using a remote-access tool in order to convince users of problems, as well as to entice the victim into buying fake repair tools in order to fix the non-existent problems.

The Federal Trade Commission states that this type of scam is one of the fastest growing cyberscams and several high-profile arrests have been made in recent times in a crackdown on the cybercriminals responsible. Technical support scams rely on potential victims being cold called and this can mean a lot of work for the scammers; however, some cybercriminals have now overcome this and have figured out a way to get the victims to call them.

When scams merge

We recently came across Trojan.Ransomlock.AM that, like its predecessors, locks the compromised computer’s screen. The locked screen displays a blue screen of death (BSoD) error message, but this is no ordinary BSoD!

In this BSoD, the message claims that the computer’s health is critical and a problem is detected and it asks the user to call a technical support number.

For the sake of research, we made a call to the number to see just what these crooks are up to.

According to the support engineer we spoke to, named “Brian,” the technical support company is called “Falcon Technical Support.” Once the number has been called, the scam follows the same modus operandi as most technical support scams; however, the most interesting thing here is the use of ransomware in order to get the user to call the scammers. Once the call has been made, the scammers have everything they need to convince the user their computer is infected with malware…because it is infected with Trojan.Ransomlock.AM.

Trojan.Ransomlock.AM

Trojan.Ransomlock.AM has been observed being distributed and bundled with a grayware installer (detected asDownloader). This installer offers to install grayware applications such as SearchProtect and SpeedUPMyPc.

Upon execution, it installs the grayware as advertised but it also drops another file named preconfig.exe, which is the malware installer (detected as Trojan.Dropper). This second installer adds an entry on the infected computer so that when it restarts it will execute the final payload (diagnostics.exe) which is Trojan.Ransomlock.AM.

Trojan.Ransomlock.AM needs an internet connection to perform its dirty deeds. The malware first needs to send information from the compromised computer to the command-and-control (C&C) server, such as the hostname, IP address, screen resolution, and a random number. In exchange, the C&C server sends back the correct size image file to fit the whole screen. The information collected will also give the crooks a useful jump start when trying to convince the user their computer is in trouble, which other technical support scammers do not have. The malware, stolen information, and BSoD lock screen all help to strengthen the scammers’ social-engineering capabilities.

Fortunately, Trojan.Ransomlock.AM was first seen in September and does not have a high prevalence; however, as with any threat, this can quickly change. According to our telemetry, the threat is currently limited to the United States.

Symantec protection

Trojan.Ransomlock.AM is far from the most complex or resilient ransomware we’ve seen and is in fact very simple. The compromised computer may look locked but users can simply follow these steps to unlock the screen:

  1. Simultaneously press the Ctrl Alt Delete keys on the keyboard

  2. Open Task Manager

  3. Search for the malware name (it should be diagnostics.exe) and end the process

  4. When the screen is unlocked, go to the registry editor by clicking on the Start button, then Run, and typing REGEDIT

  5. Delete the registry entry HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\"Diagnostics" = "[PATH TO MALWARE]"

  6. You should also delete the file folder from the directory

Users of Symantec products can simply perform a full scan to safely remove Trojan.Ransomlock.AM.

Symantec has the following detections in place to protect against this threat:

Antivirus detections

Symantec advises users to be extra careful when calling or receiving a call from a technical call center. Users should be cautious and always check the company’s identity. If you need assistance with a computer-related issue, contact a reputable bricks-and-mortar computer repair shop or your IT support team if it’s your work computer that is affected. 

Lionel Payet is a threat intelligence officer at Symantec. This post was first published in Symantec's Security Response blog, republished with permission.