Eaglercraft is a third-party project and is not affiliated with Mojang or Microsoft. The servers are not subject to Minecraft's official reporting system and may be less secure than official ones. Furthermore, since much of the project (aside from the core 1.5.2 and 1.8.8 clients) is unofficial and unsupported, there are many unofficial copies circulating. The official developer, Lax1dude, has warned that you should only use copies from the official repository and verify them with a provided PGP key to ensure the code hasn't been tampered with.

Just make sure your teacher doesn't walk behind you while you are pillaging a bastion.

The existence of Eaglercraft occupies a complex legal grey area.