You might want to look into installing an ad blocker such as Adblock Plus. Adblock Plus fetches information created by other users to block ads from web pages. The lists Adblock Plus works with are filled with thousands upon thousands lines which all contain information on which ads to block.

If you are a user of an English language version of Firefox I would recommend the Fanboy's list for your subscription. I hardly ever see a single ad online these days.

You can find Adblock Plus here: http://adblockplus.org/en/

Also what I forgot to mention is that once installed, you can simply block ads yourself if they are not already blocked.

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/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free

See also:

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