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.
A common approach is to post the logfile to a forum where more experienced users will help decipher which entries need to be removed. Automated tools also exist that analyze saved logs and attempt to provide recommendations to the user, or to clean entries automatically. Use of such tools, however, is generally discouraged by those who specialize in manually dealing with HijackThis logs; they consider the tools to be potentially dangerous to inexperienced users, and neither accurate nor reliable enough to substitute for consulting with a trained human analyst.