netsend
It's a little command line program included with windows that you can set up to send short messages to computers as a popup box. A lot of printers could use this to tell you your print job was successful, and it was used a lot in libraries and such. And also my high school. They had some cursory protections in place, but if you managed to open a command prompt you could send your own message. You just needed the recipients windows username or PC name.. our school used the standard first letter of first name + full last name, even the teachers. So of course, being highschool, this spread like wildfire and there was a whole semester where everyone was abusing it to troll other classmates or interrupt teachers mid lesson. It was also being used as IM/text before any of us even had phones - you could shoot your friend a message to dip out of class or something.
Everything came to an abrupt halt when a guy was dared to run a batch file that was a single, looped, expletive laden net send to a wildcard recipient. It sent the message on repeat to every computer in every school in the district. Every time you hit ok a new box would pop up with the same message. Supposedly every computer needed a hard restart, including servers. Dude got in trouble, and our printers stopped telling us the print job was successful after that.
The most impressive part is the lack of footprints on Amy's side. She can swing that ass like a cement truck