There was an article on it a while back:
http://it.slashdot.org/article.pl?sid=05/0...tid=220&tid=218
There was a string of ones like that for a while, some were 4 minutes, etc.. I know I've had it happen to me once when I put a freshly built PC outside the firewall for a few minutes just to test something. Took about a minute before it had got a worm of some sort.