The Trojan, identified as Cryzip, uses a commercial zip library to store the victim's documents inside a password-protected zip file and leaves step-by-step instructions on how to pay the ransom to retrieve the files.More details can be read at eWeek.
>br> It is not yet clear how the Trojan is being distributed, but security researchers say it was part of a small e-mail spam run that successfully evaded anti-virus scanners by staying below the radar.
Trojan hostages computer files and demands $300 ransom

Security experts have discovered a new Trojan that encrypts files on infected computers and then demands $300 in ransom for a decryption password: