HijackThis, sometimes abbreviated HJT, is a 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 to 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 is used primarily for diagnosis of spyware, as blind use of its removal facilities can cause significant software damage to a computer.