We used It's Learning in "high school". It had login without https at the time, and on the school wifi it was then easy to listen and get other's credentials. Some people got hold of some teachers' credentials, and tried to remove or alter some minuscule data.

One guy however, decided to sell grade-editing as a service to others. Of course it was noticed by the school, and it became a big deal with police involved and everything. Happy ending, though, the two people I know that was involved got master's in compsci a few years later.