HiJackThis
A free utility that finds malware and other threats
-- WARNING --
HiJackThis is an inactive project and it is not updated anymore. You may want to look at the existent unofficial forks though:
https://github.com/dragokas/hijackthis/
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HijackThis is a free utility that generates an in depth report of registry and file settings from your computer. HijackThis scan results make no separation between safe and unsafe settings , which gives you the ability to selectively remove items from your machine. In addition to scan and remove capabilities...