Everything.exe

Everything.exe (not to be confused with the non-malicious Everything.exe that comes with Tiny7) is a program that among other things, hijacks Windows Start Menu search to turn typed characters into the repeating string "I am a cute Eevee :3". It's designed to prevent people from rebooting the system, however, to do that, many Windows features have to be disabled. It doesn't modify any system files, so everything will return to normal if you manage to close it.

Eeveerything.exe
There's an April Fools version of Everything.exe called Eeveerything.exe. Instead of disallowing to type only in start menu, "I am a cute Eevee :3" replaces everything typed from keyboard. Though it doesn't block the computer from being rebooted, and it can be closed from the Task Manager. When this executable is ran along with Everything.exe, it makes it even harder to use the machine, though it's still possible to close both.

Eeveerything.exe and its source code (last updated 2016-04-02)