PHP.CTBLocker is a Trojan horse that encrypts files on the compromised computer and then prompts the user to purchase a password in order to decrypt them.
For more information on ransomware, see our blog:
The dawn of ransomwear: How ransomware could move to wearable devices
Definitions prior to August, 2016 may detect this threat as PHP.Cryptolocker.G.
Click for a more detailed description of Rapid Release and Daily Certified virus definitions.