HijackThis, sometimes abbreviated HJT, is freeware spyware-removal tool for Microsoft Windows originally created by Merijn Bellekom, and later sold to Trend Micro. The program is notable for taking a heuristic approach on detecting malware - rather than relying on a database of known spyware it quickly scans a user's computer, creates a list of differences from a known spyware-free environment and allows the user to decide what from the list needs to be removed.

HijackThis can generate a plain text logfile detailing all entries it finds, and most entries can be removed or disabled by HijackThis. Caution should be exercised when using the latter option, as HijackThis does not discriminate between legitimate and unwanted items with the exception of a small whitelist of legitimate entries