There are security problems in just about every language; perl is not immune to this.
I would nevertheless say that Perl is somewhat more immune
to security problems than PHP since, as I've already said in another message, PHP doesn't have a taint mode (contrary to Perl.)
(I've heard about an attempt to provide PHP with a taint mode (PHPrevent), but I think that's at present more a theoretical study than a working extension.)
Most security problems seen recently have less to do with the language itself as with bad programming practices
Taint mode is something that can help to detect and prevent such bad programming practices, and it is something that unfortunately PHP can't offer.