[Exim] Filtering against W32/Magistr?

As some people have kindly entered my address into their Windows address
books, I'm getting a fair share of infected emails. I don't really want
to expose my Windows boxes to W32/Magistr (it's nasty), but I'm not
convinced that the system filter picks them up... one got through just
now, with a "STARS.EXE" attachment.

How could filter out nasties like W32/Magistr?

--

Juha
"One pint leads to another."