Spybot - Search and Destroy is an adware and spyware detection and removal tool that can protect your system from various malware, keyloggers and other malicious programs. It offers an on-demand scan option as well as real-time protection, browser immunization and tools for advanced users.
You can perform a full system scan, which can take some time, or use a file scan to limit scanning to a specific folder.
In addition to malware scanning, Spybot provides a variety of advanced tools that allow advanced users to perform manual system inspections by investigating startup areas, browser plug-ins, HOSTS entries and other system settings.
Other features include a Rootkit Scanner, system reports, secure file shredding, and more.
Besides the free version, Spybot offers Home and Pro versions with additional features.