Brett,
Maybe I missed it, but I'm not sure I've seen a virus propagated on the
two St. John's lists I'm on.
I'm not saying it's never happened, I'm just saying that the real problem
is people and their ignorance, not listservs.
People continue to open unsolicited attachments, infect their computers,
and the worms spread.
My employer has had worms on many company computers without its users
being on even one listserv.
In short, your employer would do well to buy virus protection for its
machines rather than prohibiting this and that computing habit.
--Rick