TIP: net send * <text> sends to EVERY COMPUTER ON THE LAN. >.>
So don't do it. <.<
Don't say I didn't warn you.
Anyways, one of my profs had a VNC based app that made all the computers in the lab show what his screen showed. I figured out they did it by chaining connections... that is, Computer A would be connected to Computer B's VNC Server, Computer B woud then be viewing Computer C's server etc.
It was far to easy to break the chain tho. Win key to bring up taskbar, right click button and close. However, every 30 seconds or so the app would restart vncviewer... this was easy to defeat as well, as I could minimize the window and ignore it. In addition, it used the standard WinVNC vncviewer.exe, so I used it to connect to my own PC without having to download a viewer.
I tried to connect to the prof's PC manually with VNC viewer, but at least whoever made the VNC hack had enough of a mind to put in passwords. I could've trapped the view only password if I wanted to, but it wasn't worth my time.
A couple of friends did some really really good hacks as part of an honors thing. One of them involved bypassing BIOS blocks to boot from a CD (which was normally disabled) and partitioning and installing Linux on one of the computer lab PCs.
He also randomly found an LDAP server (at ldap.*.edu) and found it unprotected. (LDAP is used to store employee, or in this case, student information). He was able to harvest over 1000 @*.edu emails and mass-mailed them all. He is now the 4th person in the history of the school to be banned from mass-mailing.
He also installed a keylogger on one of the public PCs to pick up passwords for the school's webmail system, but he only tested it on himself and then removed it.
I forget what else he did. Some good stuff.