sounds like the conflicker virus to me...
Symptoms
Account lockout policies being reset automatically.
Certain Microsoft Windows services such as Automatic Updates, Background Intelligent Transfer Service (BITS), Windows Defender and Error Reporting Services disabled.
Domain controllers responding slowly to client requests.
Congestion on local area networks.
Web sites related to antivirus software or the Windows Update service becoming inaccessible.
Source:
http://en.wikipedia.org/wiki/Conficker