In the three weeks since I inherited the admin position at my office, the sternest warning I ever got from ClamAV was from log messages saying I had an outdated version but "DON'T PANIC." So, I think to myself, it says don't panic, so don't panic--we're going to be building a new mail server in a few months anyway, so why worry? It's not like good open-source developers would ever pull a b.s. Microsoft move like intentionally throwing a kill switch on old versions of their software.
Yeah, caveat emptor, you get what you pay for, etc. I know.