Win95, Win98, WinNT, WinMe, Windows Server 2008, Windows 8, Windows 7, WinSer2003, WinVista, WinXP, Win2k
SONAR.Cryptlk.NCod!g3 is a heuristic detection that is designed to detect known variants of the Ransom.Cryptolocker family of threats.
Disable System Restore (Windows Me/XP).
Update the virus definitions of your antivirus product.
Run a full system scan.