Virus writers are revisiting the tactic of holding data on compromised machines to ransom with a new strain of so-called "ransom-ware" Trojan.

Gpcode-AI (AKA Sinowal-FY) encrypts data on compromised machines before demanding money from users to decrypt it. The malware also include backdoor key-logging features designed to pinch confidential bank account and credit card details from compromised PCs.

When Gpcode-AI installs on the system, it encrypts every single document on the hard disk and creates a file called "read_me.txt" with the kidnappers' demands (obfuscated copy below). Prospective marks are asked to fork out $300 for a tool to decrypt the files.

Hello, your files are encrypted with RSA-4096 algorithm (http://en.wikipedia.org/wiki/RSA).

You will need at least few years to decrypt these files without our software. All your private information for last 3 months were collected and sent to us.

To decrypt your files you need to buy our software. The price is $300.

To buy our software please contact us at: xxxxxxx@xxxxx.com and provide us your personal code -xxxxxxxxx. After successful purchase we will send your decrypting tool, and your private information will be deleted from our system.

If you will not contact us until 07/15/2007 your private information will be shared and you will lost all your data.

Glamorous team

The demands falsely claim that payment needs to be made by a set deadline or else data will be unrecoverable. In reality the malware lacks any routine to delete encrypted data and the tactic is a simple ruse designed to speed up payment from victims.

The malware uses a complex encryption algorithm to encrypt user files and archives, making it impossible for victims to open files. But the Trojan uses a modified version of RC4 - and not RSA-4096 as mentioned in the text - to scramble data, according to an analysis by anti-virus experts at Kaspersky Labs. The claim that private user files might be sent to a malicious user is also false.

Victims of the malware are strongly urged not to pay money to the creators of the malware since this will only encourage further crime. Anti-virus vendors are working on technologies to both block the malware and restore scrambled data.

For example, Kaspersky Lab analysts have also created a decryption routine for encrypted files which will soon be added to its antivirus databases. Kaspersky's generic detection already spots the Trojan itself.

Other antivirus vendors are in process of adding detection for the malware strain.

Holding data to ransom using viruses to encrypt data is not a new tactic. Previous virus strains, such as the PGPCoder family, used the same tactic. Ransom-A threatened to delete a file every 30 minutes unless prospective marks paid out the relatively modest sum of $10.99. Another type of malware, Arhiveus-A, attempted to coax users into purchasing pills from an online drug story rather than asking for money directly. ®

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