Examples of extortive ransomware reappeared in May 2005. By mid-2006, worms such as Gpcode, TROJ.RANSOM.A, Archiveus, Krotten, Cryzip, and MayArchive began utilizing more sophisticated RSA encryption schemes, with ever-increasing key-sizes.
Gpcode.AG, which was detected in June 2006, encrypted with a 660-bit RSA public key. Gpcode.AK, detected in June 2008, uses a 1024-bit RSA key, which is believed to be large enough to be computationally infeasible to break without a concerted distributed effort.
simple method for those who aren't comfortable in command lines etc.
How to remove ransomware virus in windows xp
For Hiren boot cd in win7 users the ransomware file is located C:\Users\your account\AppData\Roaming
Boot pc into safemode with networking by pressing f8 key
Second download Malwarebytes run updates and a full scan then quarantine the virus
lastly download superantispyware and do the same thing.