How do I know my computer is virus free?

I have Norton Internet Security installed on my computer but sometimes it has got too slow than before (I had it for a year and a half now). Is there any programme which I can use to determine that my computer is threat free (virus, hijacking etc. etc.) while keeping Norton installed.

I have done the msconfig thing and unchecked the unnecessroty programmes.

How do I know my computer is virus free?hp

Install some anti spyware, trojans and spyware are much more common than viruses now! It won't conflict with your firewall or anti virus.

You need all these anti spyware programs;

http://free.grisoft.com/doc/20/lng/us/tp... - AVG anti spyware

http://www.safer-networking.org - Spybot Search and Destroy anti spyware. Use the Teatimer settings to protect Internet Explorer, and the Immuniser to stop malware getting on your pc.

Spywareblaster works with Internet Explorer and Firefox. It won't uninstall spyware that is already on your pc, but it will prevent hijacks and other malicious changes to your browser.

http://www.javacoolsoftware.com

Plus;

http://www.lavasoft.com - Ad-Aware SE Personal anti adware

Also, run Ccleaner, use the Issues tool and then the Cleaner.

http://www.ccleaner.com

Defragment the hard drive from Start - programs -accessories - system tools - disc defragmenter. Leave the pc while it runs and do it once a month.