Ad-Aware is a popular anti-spyware product made by Lavasoft. This protects Windows PCs from adware. Adware is a term for programs that installs themselves on your PC and show you ads – it’s generally a bad thing.
They’re just released version 8 which they’re calling their Anniversary Edition. They have a free edition and 2 paid editions, each with different features.
If you download the free edition remember that you’ll need an anti-virus program on your PC (one that scans web pages as well as your PC).
Main Ad-Aware web page (has all 3 editions): http://www.lavasoft.com/products/ad_aware.php
Direct download to the free version: http://www.download.com/Ad-Aware-Anniversary-Edition/3000-8022_4-10045910.html?part=dl-ad-aware&subj=dl&tag=top5&cdlPid=10998841