This is rapidly becoming off topic, but I wanted to mention that hardware firewalls often may be configured to block certain ports at particular times of day. For example, I have a Netgear WGR-614v4 -- It allows me to block access to the Internet entirely, based on time of day, or to just block certain ports (for example, AIM).

A hardware firewall is often a simple, foolproof, and robust solution. My particular hardware router isn't unique in these capabilities; most consumer hardware routers have pretty good firewalls built in.

As far as using Perl, the problem is that software firewalls are very low level. They must place themselves between the OS's networking layer and any (and all) software running on the computer. It's a tricky thing to do, and for the most part, better done in a systems language. ...at least when speaking of software firewalls on non-dedicated systems.