Risk: Medium
Trojan holds PC files for ransom.
A unique new kind of malicious threat, which locks up files on a PC then demands money in return for unlocking them has been identified.
The program, Trojan.Pgpcoder, installs itself on vulnerable computers after users visit certain web sites.
It exploits a known vulnerability in Microsoft's Internet Explorer (IE).
Apparently, the program had not spread quickly, but is another example of rising criminal extortion activity on the net.
The malware - harmful software - was first identified by US Internet security firm Websense.
The program, once it installs itself unbeknown to the user, triggers the download of an encoder application, which searches for common types of files on a computer and networked drives to encrypt.
When a file is encrypted, usually for security and privacy purposes, it can only be decrypted with specific instructions.
The Trojan replaces a user's original files with locked up ones, so that they are inaccessible. It then leaves a "ransom note" in a text file.
Instructions to release the files are only handed over when a ransom fee is paid, according to Websense.
The electronic note left on the computer gives details of how to meet the demands via an online account.
"This attack is yet another indicator of the growing trend of criminals using technology for financial gain," said Kevin Hogan, senior manager at web security firm Symantec.
"This Trojan horse is certainly an example of using cryptography for malicious purposes.
"It is the equivalent of someone coming into your home, locking your valuables in a safe and refusing to give you the combination."
But because it does not send itself out to contacts that a user might have stored on a computer, it is classed as a Trojan. This limits its ability to spread around to high levels, "in the wild", said Symantec.
Computer users are urged to ensure their anti-virus and security software is up-to-date.