What does an on line scan do?

I have AVG Anti virus (paid version) and I use AdAware free anti spyware.I scan with AVG about at least once a day,and I scan with AdAware twice a day.But sometimes I see ads offering free on line scans,is this something I should do? or just stick with what I've been using?

What does an on line scan do?photoshop

As jibbarjabar says, neither AVG anti-virus nor Ad-Aware are best of breed so a periodic on-line scan isn't a bad idea, provided it's from a reputable company.

Nearly all AV programs you can install on your computer run in real-time mode, which means they *should* prevent viruses/malware getting on your pc.

Online scans are only re-active, they can't prevent it getting on but they *may* find anything your anti-virus or anti-spyware program has missed.

Some of the online scans will only find malware and won't remove it (e.g. Kaspersky). Some will find and remove (e.g. BitDefender %26 NOD32).

Also, there are scam scans which will claim to find many 'viruses' in the hope of frightening you in to buying their piece of crap.

Generally, the anti-spyware programs you can buy are pro-active, the freebies are re-active. So, if you're using a re-active free anti-spyware program, consider also using SpywareBlaster. This doesn't scan your pc, instead it keeps a lot of crap from installing in the first place.