Hijack This

HijackThis, sometimes abbreviated HJT, is free ware spy ware-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 spy ware it quickly scans a user's computer, creates a list of differences from a known spy ware-free environment and allows the user to decide what from the list needs to be removed.

Use:
HijackThis can generate a plain text log file 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 white list of legitimate entries — thus allowing a user to unintentionally disable important programs from running, which may possibly cause their system or peripherals to stop working. HijackThis will, however, attempt to create backups of the files and registry entries it removes, which can be used to restore the system in the event of a mistake.

A common tradition is to post the log file to some web board/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 analyzer.

Later versions of HijackThis include additional tools like a task manager, hosts file editor and alternate data stream scanner.

The below shown video will explain us a better usage of this tool, this tool can also used with windows vista. This video belongs or copy rights belong to CNET.Com.
Thanks to TOM again.

You can download the HijackThis from www.download.com, www.filehippo.com or also from www.trendsecure.com