Please note: No single Virus Scanner is ever 100%
Safe Surfing is always a must and will keep you virus free far better than any scanner.
You should never install more than one Scanner on a single system.
They will fight and conflict and cause problems.
The problem you had with Norton, they are notorious for, them and McAfee, killing all network connectivity out of the blue, till uninstalled.
My Parents had free McAfee (about a month ago) and all of a sudden internet stopped, no printing wifi. Uninstalled McAfee, and everything worked.
Those have been an issue for a very long time. When I first had the issue (Norton) some years ago, I had not made any changes or blocked anything, I spent several hours trying to fix it. Uninstalled permanently and have never had that problem since.
AVG I wouldn't touch If I was paid to do so.
I have seen massively infected systems that had AVG installed and the only time AVG said anything was when the system was scanned by another scanner. BTW, the system with the most virues not detected by AVG when it was running and even after doing a manual scan and finding nothing was 4000+ items ( not all the same virus, many replicants, but not all of them) and none were cookies. I stopped the system and burned them to a CD we were going to use ourselves to test AV, but never got around to it and I don't have it anymore.
Kaspersky is very good, but has had performance hits in the past and I suspect that hasn't changed much
Avast is good, but experienced the same, not as bad as Kaspersky, but...
Eset i have not checked out in a long time. Might want to take a look at them.
AV-Comparatives - Independent Tests of Anti-Virus Software ... then click on Comparatives
The tests out there are a bit dated, but they stand up to today.
I would also stay away from Trend Micro and Webroot.
For on-line scanners I would recommend...
ESET Online Virus Scanner | ESET
Microsoft Safety Scanner - Antivirus | Remove Spyware, Malware, Viruses Free --- I ran this prior to posting to this thread and it does run in Win8.
Panda Activescan | Free Online Antivirus | Free Virus Disinfection - Panda Security -- I believe this is their On-Line Scanner.
Kaspersky Security Scan | Kaspersky Lab United States
For all on-line scanners, I would check that nothing remains behind in Programs and Features, uninstall it if there is.
It is always a good idea to run at least one of these every so often.
You should not need to disable or uninstall any current anti virus you may be running when running an on-line scanner.
These are a one shot run.
Also note that things that can be detected and look like viruses are really cookies that will go away by clearing Temporary Internet Files and Cookies.
Hope this helps.