You can use POP3 as well, but the messages will just be tagged with [spam] in the subject or something. Personally, I'm not a huge fan of Razor, although the new versions do have some improvements.
You may want to consider a server-side or client side filter that uses adaptive (Bayesian or pseudo-Bayesian) technology; bogofilter is such a system to run on the server-side, although there are some unfortunate file locking problems that cause problems on our system. The Mozilla mail client and Mail.app both have decent built in adaptive filters.
SpamAssassin is another program that's been mentioned. The version installed on our mail machines is old, so I'd suggest installing your own version. This does require a certain amount of tech-savvy though, and (mostly due to its resource consumption) we don't plan on implementing it server-wide at this time.
Note that spam filters will not always catch viruses; the message you're talking about is a virus, not spam (btw, the spam reporting address is just for spam, not for viruses).
With stuff like this, you may be able to define a simple filter in the mail filters panel (or using procmail recipes if you're inclined to "diy"), as the messages will usually contain one of a fairly small subset of strings.
We don't do a lot of blocking of viruses except in certain extreme cases (in retrospect, the virus you're speaking of probably was such a case). I don't like silently discarding messages, and blocking them at the border with a 5xx error tends to cause weird problems with Yahoo groups when viruses get sent through the list. Occasionally, the patterns we use to block a virus ends up existing in a regular email.
I know that a lot of spam and viruses still get through, but believe me - we reject a lot of incoming spam. One recent informal check I did showed us rejecting about 40% of incoming mail due to UBE restrictions. Implementing better spam and virus filtering is something we're working on.
I'm hopefully going to get up a kbase article explaining some of these restrictions in more detail.