I put source other than above because I thought its bound to be something clever like mainstream Software Downloads / patches. That said I would of thought popups, other areas where you have to click on dodgy adds, would be the worst

I'd be interested to hear some stories as well, AV Management is a big part of my job.

The majority of virusses spread via pirated software and other crap people download over P2P networks.
Email virusses used to be big but have been on the decline for a year or more.

Direct infection through websites is low and generally not viral in nature but limited to installation of spyware or trojans that are usually not self replicating (though they may take actions to trick others into infecting themselves) and therefore don't class as virusses.

file sharing networks. I think 50% of files on kazaa are corrupt.

At one point security firms estimated 90% of files on Kazaa had malicious payload.
I believe it's gotten a bit better but noone's ever done a similar survey on bittorrent and similar networks AFAIK.

My PC used to be spyware-ridden and I only used internet explorer and a very inactive hotmail account. Coincidence? I think not. Explorer is definitely to blame.

You can play 'games' with voting and listening to uninformed opinion, but if you listen to this fella instead you'll get the truth!

No, listen to me for the truth

Viruses may spread through P2P networks, but they originate in the computer of an evil computer hacker (see here). Then that hacker sends it to someone, who sends it to someone else.... you get the point.

Mean people write them, of course. They aren't just spontaneously generated.

Then those people sneak them into innocent looking software and trick you into downloading the software.

Or they email you a link that downloads a virus.

Microsoft is the real culprit, by making Windows so it can run software from a remote source.

uh, the first virusses ran on Unix computers in the 1970s...

They were intentionally created and non-mallicious (except for slowing down network traffic). Their goal was to spread updates to software automatically to all users whereever they might be. Problem was they were too effective at spreading

The first recorded mallicious virus for DOS was created unintentionally when a university student in Jeruzalem made a programming mistake.