Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/security/scanner/en-us/default.aspx - Microsoft Safety Scanner
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy

You can also do a check for a rootkit infection with TDSSKiller.

• http://support.kaspersky.com/viruses/solutions?qid=208280684

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

Running a malware program/application may not fix the problem if your infection is the malware listed in the following article. You may need to download and run some other items before the malware program(s) to reverse some of the changes made to your system. Review the following article carefully, and if the screenshots near the top of the article look familiar, follow the instructions given in the order given to rid your system of this pest.

• http://www.bleepingcomputer.com/virus-removal/remove-win-7-antispyware-2012