Virus scan issues

[txzen]

So, I've had a sudden degredation in the way my computer is working - very slow and jerky when accessing the internet. I run the Norton Firewall and Antivirus software, which are regularly updated. A full scan (in normal and "safe" mode) found nothing.

I used a few of the web-based virus scans, and infected files (as many as 7) were detected. The most complete list was found by the McAffee online scan. Heck, even the Norton site found one.

On advice, I downloaded the AVG free antivirus program and...it found nothing (in normal or safe mode). I'm going to buy the McAfee software today, and uninstall the Norton stuff (fed up with Norton for different issues), but my question is...

Why is this happening? Why are the web-based scans finding these trojans and my onboard software isn't?

 

[zzzz]

I read the other day in the WSJ that both McAfee and Norton detect competitor's products and sometimes suggest disabling components of them because they may be a security risk. Perhaps some of the files McAfee detected were related to Norton.

Oh, btw, make sure you use only reputable online scanners:

NOT something like StopSign

In reply to:

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[TexasOwnzYou]

i think a seperate trojan scanner is more powerful for finding trojans (and removal) than a regular AV (like norton/mcafee)

i had a trojan once and i had to use a specific anti-trojan (The Link ) to remove it.

 

[txzen]

I don't think it was a conflict issue. I did disable my Norton while running, and the files (and viruses) were specified as these Java/Shinwow trojans.

I'm also off to buy a hardware firewall. I'm going with suspenders and a belt now.