Trojan:WinNT/Sirefef.C is the detection for a driver component that is used to inject code.
Trojan:WinNT/Sirefef.C is dropped and installed as a system driver service by other members of the Sirefef family, such as TrojanDropper:Win32/Sirefef.B.
Trojan:WinNT/Sirefef.C attemps to inject code to any process that loads the system file "mswsock.dll". This DLL is usually loaded when the process needs to send or receive network packets.
Analysis by Chun Feng
Alert notifications or detections of this malware from installed antivirus or security software may be the only other symptoms.