There was no recent software installation or other system change that prompted this. Windows updates may have occurred.
I verified the screen saver setting. I even set and cleared it to flush out any corrupt settings.
I rolled back several days of system files and settings, in succession.
MS Security Essentials, running in Safe Mode and doing a full systems scan, found and removed a virus rated 'severe': Trojan.js/Redirector.EV.
Windows 7 Ultimate, everything up to date.
A Google search did not come up with any advice. A virus with similar behaviour is described for XP only, and the remedy applies to XP only.
I assume this is a virus since I cannot determine any system setting or software change that could be the cause of this problem. How can I fix this?
I consider myself a competent user, happy to examine registry and startup settings safely.
Thanks, any advice greatly appreciated. i will continue by rolling the system back even further and employing alternative virus scanners.