Per Ken Blake:
I think
that that's one of the most dangerous pieces of advice you see around,
because it implies that it's safe to do the opposite--open attachments
from friends and relatives. But many viruses (and other kinds of
malware) spread by sending themselves to everyone in the infected
party's address book, so attachments received from friends are perhaps
the *most* risky to open.

That happened to me at a place where I was doing contract programming.

Reasonable-sounding Subject line, reasonable-sounding message, somebody
I knew.... so I opened the attachment.

Won't go in to what happened next, but thankfully the AC power plug to
my PC was within easy reach...... And if somebody from the client had
been walking past before I managed to pull it, I would have found myself
out on the street within minutes.
--
Pete Cresswell