HijackThis is a free utility by Trend Micro which heuristically scans your computer to find settings that may have been changed by homepage hijackers, spyware, and other malware or unwanted programs.
This application has a well deserved reputation for being aggressive in tracking down unauthorized changes that have been made to your system/applications.
The program doesn’t target specific programs, but instead it analyses registry and file settings and targets the methods used by hijackers to redirect your browser. After the scan HijackThis creates a report, or log file, with the results of the scan.
Because of the heuristic methods used by HijackThis, the results of the scan can be confusing to those who are not advanced users. However, the strength of this program lies in the large community of users who participate in online forums, where experts will interpret HijackThis scan results for you, and provide you with the information you need to clean any infection.
There is a great tutorial on using HijackThis at BleepingComputer
The latest version (2.0.2), adds powerful tools to the Configuration window including, a process manager and hosts file editor to help you excise virulent infections, and the ADS Spy tool which scans alternate data streams, that browser hijackers can use to evade spyware removers.
Despite the fact that you may only need this small application infrequently, it deserves a place in your anti-malware toolbox.
System requirements: Windows Vista, XP, 2000, Me, 98
Software requirements: Internet Explorer 6.0 or 7.0, Firefox 1.5 or 2.0
Download at: Trend Micro