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Guster Ransomware

Posted: December 23, 2016

Threat Metric

Threat Level: 10/10
Infected PCs: 92
First Seen: December 23, 2016
OS(es) Affected: Windows

The Guster Ransomware is a Trojan that blocks your files and your desktop with a combination of data-encrypting and pop-up attacks. Its threat actors use these attacks for soliciting Bitcoin payments that supposedly will unlock your screen and your data. For most PC users, other recovery options are freely available, provided that you use appropriate security procedures for disabling and removing the Guster Ransomware with a dedicated anti-malware application.

Another Hidden Tear Trojan Comes out of Hiding

Social manipulation plays an important part in many threat campaigns, including the different releases of Hidden Tear-based threats malware analysts see each week. You can see many of the 'nagging' techniques con artists use in the new the Guster Ransomware campaign, which gets its ransom money from locking your files and, then, selling the unlocking service. As a far cry from its simpler, text-based brethren, this Trojan includes such elements as a timer, audio and semi-advanced graphics.

The Guster Ransomware's data-locking attacks still have a basis on the AES encryption, which enciphers your files on a format-by-format basis, rendering them unable to be read or opened. After locking the files and inserting the '.locked' extension at the end of their names, the Guster Ransomware launches a desktop-blocking window containing its ransom demands and other features.

Instead of a simple Notepad TXT file, the Guster Ransomware uses an advanced HTML Web page for delivering its extortion demands (0.4 Bitcoins, equal to 360 dollars) for restoring the encrypted content back to normal. Signature elements of the pop-up include:

  • The Guster Ransomware uses a default text-to-speech feature to warn you that your data is locked by a 'strong military cryptography' in a repeating audio loop.
  • The Trojan's pop-up also adds timing-based elements as a numeric countdown and a progress bar. It's payment instructions bolster this theme with repeated warnings that ignore the time limit that will cause the threat actor to 'blow up' your data.
  • It provides other formatting elements for engaging the victim visually, including a gas mask-themed background image, flashing font colors and an animated GIF. Note that the background image is one that malware analysts connect to other Trojan campaigns, although this recycled component doesn't imply any direct relationships between the Guster Ransomware and other threats necessarily.

Getting out of a Ransomware Loop

The Guster Ransomware uses multiple methods of psychological manipulation for engendering impatience and fear into its victims while it keeps them locked out of both their files and the rest of the PC's user interface. For families of file-encoding threats with free decryption help available, such as the Guster Ransomware and the rest of the Hidden Tear family, victims should attempt these solutions before considering paying any ransom money. Otherwise, backups not compromised by the Guster Ransomware may be the only guaranteed means of recovering any enciphered data.

Since the Guster Ransomware uses its ransom message to block your screen, malware analysts suggest disabling the pop-up window before disinfecting your PC. Rebooting in Safe Mode or through a peripheral device can launch your operating system without also launching this Trojan or related threats. Anti-malware utilities, while not able to decrypt any '.locked' content still may remove the Guster Ransomware so that you can implement other recovery steps.

Notably, although the Guster Ransomware's warnings are visually and audibly intimidating, the Trojan doesn't include an auto-delete function for any of the local content. The time pressure is, as always, more of another way of tricking the victims than anything else.

Technical Details

File System Modifications

Tutorials: If you wish to learn how to remove malware components manually, you can read the tutorials on how to find malware, kill unwanted processes, remove malicious DLLs and delete other harmful files. Always be sure to back up your PC before making any changes.

The following files were created in the system:

file.exe File name: file.exe
Size: 3.06 MB (3065344 bytes)
MD5: ec2a8d8f7853397f86a4c96fdbe01b19
Detection count: 48
File type: Executable File
Mime Type: unknown/exe
Group: Malware file
Last Updated: December 23, 2016