Best virusscan?

[Fyron]

If you really feel you must waste money, it appears that NOD32 is near the top from the test results I linked to earlier, and I tend to see it recommended more than Avira... But I still suggest not wasting money on AV, since the free ones are just as effective if you practice safe computing.

[AstralWanderer]

AV Comparatives provides one of the best tests of AV performance (their last one used almost 500,000 items of malware) so should be worth a look. Kaspersky tends to do best on straightforward scans (and it includes other features like Proactive Defense that can limit what unrecognised malware can do) while NOD32 does better at the retrospectives (tests using 3 month-old signatures on newer malware to see how scanners' heuristics cope with unrecognised items).

AV-Test.org is another major testing body, producing reports for other publications (a recent example being this PCMag AntiVirus Roundup).

Wilders Security has an AV Software subforum for more discussion of these (and other) results.

[Fyron]

Kaspersky is really, really, really slow at scanning.

[AstralWanderer]

Imperator Fyron: Kaspersky is really, really, really slow at scanning.

Recent versions (2006 onwards) have greatly improved on this, by keeping a checksum of files already scanned so they only get scanned again if their contents change. In most cases, there should be no noticeable slowdown once a full scan has been performed.

Kaspersky does include over 200 unpackers in its scan engine so that will account for slower scan speed compared to many others, but for high-risk Internet users, a better detection rate for encrypted/modified malware (which is the main threat currently) is likely more important. For faster scanning, the likes of NOD32 would be a better choice though NOD32 has itself become slower due to the need to handle more unpackers.

[Arralen]

Use Norton products.
Oh, yes, I'm making my living from fixing other people computers.

Just in case you live too far a away from me to call me for help when the next trojan has taken over you system, I would recommend
Kaspersky Internet Security Suite, though

Simply scanning files for malware isn't enough any more, you actually need something that scans files as soon as they're coming in from the net: there's a small time window between e.g. the browser loading images and scripts from the internet and them being written to the cache file on disk (and thats where traditional scanners come in). Most exploits (other than "clickme.exe, I'm a bill in pdf format") happen by breaking in through buffer overflows etc in scripts, pictures etc when those are loaded into the rendering engine for display. At the time they're written to disk cache, the scanner might already be taken out be the malware.

Btw., forget all the marketing blurb and "need no firewall"-flamers .. you need a firewall - to block access from the outside. As soon as any malicious software runs on your system, it will find a way to connect out and maybe even load additional modules.
The build-in XP firewall (comes with Service Pack 2) denies ports/service access from the outside - but that's it. It does neither control outgoing requests nor requested incoming traffic at all. While the first is impossible to do (as I said above), the assumption that all incoming traffic the is requested is legitimate doesn't hold true any more: a "trustworthy" website might have some adds displayed from another server which in turn has been hacked, and some of those adds images manipulated to exploit some security issue.

Conerning free vs. paid scanners:

ClamAV sucks.
At first, it does not have an online scanner: It does not even check files written to the browser cache unless you stop surfing and manually scan the cache folder. Not very effective. Ok, it has been developed as email-scanner running on linux servers, therefore this might be ok.
But I have to submit virus samples to them regularly which where recognized by Kaspersky or even "Eyeball MkI" but not ClamAV ...

AVG ....
At first, they do a really good job of hiding their free product. And they issue conflicting statements how long (if at all) it will be supported any longer.
Only plus I know: they still support Win98, in case anyone uses that to access the internet, what is slightly insane in itself anyway...

Avira (Antivir)
It's barely ok if you're behind a router (replaces firewall), using Firefox with noscript and addblock extension and running a restricted user account on W2K/XP professional, which access rights set up properly. Detection rates are not as good as with Kaspersky.
On the plus side, it doesn't interfere with gaming as it's online scanner is very fast.

[narf poit chez BOOM]

Thanks, everyone.