This is the list of the 4 useful softwares for windows users. Read complete post for details.
- Belarc Advisor - Free Personal PC Audit
- HijackThis
- System Mechanic
- Spybot - Search & Destroy
Belarc Advisor - Free Personal PC Audit
Price: Free 
The Belarc Advisor builds a detailed profile of your installed software and hardware, missing Microsoft hotfixes, anti-virus status, CIS (Center for Internet Security) benchmarks, and displays the results in your Web browser. All of your PC profile information is kept private on your PC and is not sent to any web server.
This kind of software is more useful for those who own assembled PC and dont have the complete specification of the various h/w used.
