An essential tool for Windows users as Windows and Internet Explorer leave detritus and there is no bio-remediation process (like maggots for cleaning the skull of a trophy or manure for the compost heap).

Download from FileHippo, install without the Yahoo Toolbar. Turn on the Advanced Options, in Options, Advanced check "Hide Messages, uncheck the rest. "Run Cleaner", reboot and do it again. Repeat for every user on the machine.

Switch to Registry, Scan for Issues, Fix all Issues. You will want to repeat this process later. This will remove dangling references to Virii and Trojans you have already removed.

Click Tools and run the Uninstaller for every package you do not need. This is a judgment call, but for the most part you can reinstall over zealously removed packages

CCleaner not only removes bad programs laying around in Temporary Internet Files and the like but reduces the load of items to scan in other Antivirus programs.