According to Kaspersky Lab (June 5, 2008), the new Virus.Win32.Gpcode.ak variant is said to take your personal files hostage by encrypting them with a 1024-bit key, a huge upgrade from the previous Gpcode variant which was using a 660-bit key.

You will be able to identify if you’re infected with Gpcode when you notice your personal file has an extension of ._CRYPT and has text file named !_READ_ME_!.txt in the same folder.

Kaspersky Anti-virus users are protected from this variant since June 4,2008.

Further reading at Gpcode: the return of the file encryptor by Kasperky Lab Weblog.