http://edshowtos.blogspot.com/2008/06/how-to-make-your-own-n... (NES)
http://forums.benheck.com/viewtopic.php?t=35526 (SNES)
You can find a bunch of other hacks like this on HaD:
Maybe it was the mouse. Damn.
http://www.irongeek.com/i.php?page=security/programmable-hid...
In that case, compromising one of the clients behind the firewall is the typical next step for an attack. (They did a heck of a nice job on that, though.)