These are some common/standard port number for "pass-thru" on a proxy or firewall. These are meant simply as a guide, and not a recommendation.

In addition, any network/security administrator with a little knowhow, can of course change these numbers. For example, you dont HAVE to have the http port as 80, you can always change it. Sometimes that will be enough to keep some "innocent" hackers away (like school students, or newbies). It wont however, fool a port scanner, or a "tried and true" hacker.

Remember that ANY port you open up for access, becomes a port for a hacker as well. It is a double edged sword.