Ad-Aware
http://www.lavasoft.com/products/ad_aware_free.php

ad_aware_logo.jpgAbout Ad-Aware: "We have taken the security product millions of people know and trust one step further to give all users the power to protect themselves. By combining Lavasoft's pioneer anti-spyware technology with advanced Genotype detection, Ad-Aware Free is your proactive malware removal tool, allowing you to combat today's toughest cyber threats. Ad-Aware Free Anti-Malware features real-time protection, a rootkit removal system, automatic updates, and much more — to ensure that you have the power to protect yourself online. A power-packed combination of our pioneer anti-spyware technology together with rootkit protection and advanced Genotype detection to provide proactive malware protection, including protection against spyware, blended malware, trojans, rootkits, hijackers, keyloggers, and much more. Integrated real-time process protection blocks malicious processes and infected programs that try to start or run on your system, to prevent them from further integration in your system. Cutting edge anti-rootkit technology protects you from hidden threats and stealth attacks that are designed to gain access to your system by avoiding detection."