Cryptolocker

Overview
Cryptolocker was a highly sophisticated ransomware that used cryptographic key pairs to encrypt the computer files of its victims and demanded ransom for the encryption key. In June 2014, the FBI announced (in conjunction with the Gameover Zeus botnet disruption) that U.S. and foreign law enforcement officials had seized Cryptolocker command and control servers. The investigation into the criminals behind Cryptolocker continues, but the malware is unable to encrypt any additional computers.

Source

 * Ransomware on the Rise: FBI and Partners Working to Combat This Cyber Threat.