I became a lot engaged more in class after realising I could remotely shutdown the teacher's computer with a custom message.
In middle school our entire school network was running some strange windows server p2p setup. What this means is that any computer could issue commands across the network to other computers, purely by knowing the name of the port. Luckily, every ethernet "outlet" had a label stating the port's name. This made it stupidly simple to issue a `shutdown \M <PORT>` in the middle of class.
Omg, I know I did this, but throw a double proxy. I thought a special education pupil howto remote shutdown and wrote a script. I told him they'd know it's him. So we scripted the Internet Explorer icon with a pre-exec command script, that basically did a network-scan for IPs and shutdown each one remotely. Poor fella sitting there didn't even know what's happening. Was a bully, but still. They interrogated him and he didn't even know what happened.
We sat there and saw every computer at the school turn off with a custom message. Except his computer. He really looked dumbfounded.. I get a smile when I think of it.. it wasn't anything evil or bad, but just fun.
Good 'ol times. He didn't get into any trouble, just disciplinary extra curricular work. Which I think was good for that bully anways.. he was lacking behind.
Also I remember accesing everyone $C drive and copy a counter-strike map of the school I was modeling into. So, the next time anyone went to a LAN-Party (THOSE were GOOD Times), everyone would see the school name as a map and nobody would know who made it. Obviously no violence intended. I just wanted to play in an environment that I spent most of my day and have fun afterwards at they way we could have some fun. Asking everyone to download it would've just led to trouble. Of course I heard of school shootings, but counter-strike was harmless. Those who did think of worse had this in mind anyways.