Malicious software ("malware") could be installed on your computer.
Make sure that your anti-malware software is running, then download the
latest signatures and run a full scan.
Comprehensive anti-malware software scans for all types of malicious
software in the background, on demand and on schedule. If you don't have
comprehensive anti-malware software, you're a sitting duck.
For now try scanning your system with /several/ of the better online
scanners, such as:
Kaspersky Antivirus (
http://www.kaspersky.com/virusscanner)
Panda ActiveScan (
http://www.pandasoftware.com/activescan)
Download HijackThis from
www.trendsecure.com. Run it, save a log, and
post the log at one of the many sites that support HJT, such as
spywarewarrior.com, bleepingcomputer.com, and
http://aumha.net -- but
not here. Within a day you'll have step-by-step advice from an expert on
cleaning up any malware infestations.
Even the best detection and removal software can't fix every malware
infection. If none of the above remove the infection, you may want to
show the computer to a professional. You might need to erase your hard
drive and start over.
