Bypassing firewall

[Mailing Lists <mlist () almerco ca>]

Hi!

Back where I work, we are using a firewall the blocks everything coming in, 
and gives internal users permission to use the www, ftp, pop and mail 
ports.  (no icq, no aol, no nothing else).

But I overheard one of my users bragging that it bypassed the firewall 
using two linux machines doing port redirection.

I did a little research on this and the most plausible way I found is that 
he is running a linux inside the firewall which grabs everyhing on a 
certain port (let's say the icq server port), then forward it through port 
80 to another linux box outside the firewall which make the actual call to 
the icq server on the right port.  Is that possible?  Is there any other 
alternatives he can be using?

btw, I don't know what the firewall used is, I'm the sysadm for my 
division, but we are using the corporate firewall.

Thanks!