Is there anything that could ever be done to prevent a Perl virus from running?
Well, I would like to offer my suggestions.
Make an unprivileged user and call it "scriptGuy" or something
Remove all of that users privileges everywhere, and I mean EVERYWHERE.
Begin restoring privileges to that user on a need-by-need basis until it becomes a semi-usable account
Run all scripts as that user
Never run code found in the wild without understanding it or, at least, trusting the source from which it came
Now, this discussion is going to easily turn into a general discussion on computer security (i.e. shut off ftp and telnet, use ipchains, etc., etc.). But, that might not be such a bad discussion to have.