When I was in 11th class, my school got a new setup for the school PCs. Instead of just resetting them every time they are shut down (to a state in which it contained a virus, great) and having shared files on a network drive (where everyone could delete anything), they used iServ. Apparently many schools started using that around that time, I heard many bad things about it, not only from my school.
Since school is sh*t and I had nothing better to do in computer class (they never taught us anything new anyway), I experimented with it. My main target was the storage limit. Logins on the school PCs were made with domain accounts, which also logged you in with the iServ account, then the user folder was synchronised with the iServ server. The storage limit there was given as 200MB or something of that order. To have some dummy files, I downloaded every program from portableapps.com, that was an easy way to get a lot of data without much manual effort. Then I copied that folder, which was located on the desktop, and pasted it onto the desktop. Then I took all of that and duplicated it again. And again and again and again... I watched the amount increate, 170MB, 180, 190, 200, I got a mail saying that my storage is full, 210, 220, 230, ... It just kept filling up with absolutely zero consequences.
At some point I started using the web interface to copy the files, which had even more interesting side effects: Apparently, while the server was copying huge amounts of files to itself, nobody in the entire iServ system could log in, neither on the web interface, nor on the PCs. But I didn't notice that at first, I thought just my account was busy and of course I didn't expect it to be this badly programmed that a single copy operation could lock the entire system. I was told later, but at that point the headmaster had already called in someone from the actual police, because they thought I had hacked into whatever. He basically said "don't do again pls" and left again. In the meantime, a teacher had told me to delete the files until a certain date, but he locked my account way earlier so that I couldn't even do it.
Btw, I now own a Minecraft account of which I can never change the security questions or reset the password, because the mail address doesn't exist anymore and I have no more contact to the person who gave it to me. I got that account as a price because I made the best program in a project week about Java, which greatly showed how much the computer classes helped the students learn programming: Of the ~20 students, only one other person actually had a program at the end of the challenge and it was something like hello world. I had translated a TI Basic program for approximating fractions from decimal numbers to Java.
The big irony about sending the police to me as the 1337_h4x0r: A classmate actually tried to hack into the server. He even managed to make it send a mail from someone else's account, as far as I know. And he found a way to put a file into any account, which he shortly considered to use to put a shutdown command into autostart. But of course, I must be the great hacker.