All of these are ones that I personally use and all are free.After you install any of them,make sure you update them to get the full affect.
Download Grisoft AVG 7.5 Anti-Virus,Anti-Malware.(free)
AVG is a collection of anti-virus protection tools that gives you full protection against viruses, worms, Trojans and malware. AVG provides you with all that you need to be completely protected: including a tool for scanning your hard drive and e-mail, as well as a real-time shield to prevent infections.
Top Features
» Provides automatic update functionality
» Its a reliable anti-virus scanning engine
» Provides free Virus Updates for life
» Options to define file name extensions
» Real time protection with resident shield, email scanning
http://free.grisoft.com/doc/5390/lng/us/...
Spybot - Search & Destroy detects and removes spyware, a relatively new kind of threat not yet covered by common anti-virus applications. Spyware silently tracks your surfing behaviour to create a marketing profile for you that is transmitted without your knowledge to the compilers and sold to advertising companies. If you see new toolbars in your Internet Explorer that you haven't intentionally installed, if your browser crashes inexplicably, or if your home page has been "hijacked" (or changed without your knowledge), your computer is most probably infected with spyware. Even if you don't see the symptoms, your computer may be infected, because more and more spyware is emerging. Spybot-S&D is free.
http://www.spybot.info/
http://superantispyware.com/
SUPERAntiSpyware is the most thorough scanner on the market. Our Multi-Dimensional Scanning and Process Interrogation Technology will detect spyware that other products miss! SUPERAntiSpyware will remove ALL the Spyware, NOT just the easy ones!
Easily remove over 100,000 pests such as SmitFraud, Vundo, WinFixer, SpyAxe, SpyFalcon, WinAntiVirus, AntiVermins and thousands more!
Yahoo toolbar offers FREE anti-spyware:
Scan your computer for potentially destructive programs.
Review suspicious-looking programs.
Remove the programs you don't want. Keep the ones you do.
http://new.toolbar.yahoo.com/toolbar/features/norton/
Here is another free anti-virus-
PC Tools AntiVirus Free Edition feature highlights
Protects your PC as you are working, surfing and playing
Detects, quarantines, disinfects and destroys Viruses, Trojans and Worms
OnGuard™ protects your computer against threats in real-time
Automatically checks for frequent updates against the latest threats.
http://www.pctools.com/free-antivirus/
Pc Tools also has a free firewall.
*Never install more than one anti-virus on your PC, as they may conflict with each other. On the other hand, its always good to install more than one anti-spyware.