If you have Microsoft Security Essentials and today (September 30, 2011) it detected the PWS:Win32/Zbot virus it may be a false positive. Especially if it seems to be shutting down Google Chrome.

MS suggests updating the Security Essentials definitions to fix the problem.

References:

http://www.microsoft.com/security/portal/Threat/Encyclopedia/Entry.aspx?Name=PWS:Win32/Zbot