Back in the day with Windows 95/98 you used to be able to send network messages to individual users that looked like they were coming from a server/network admin. To the trained eye you could tell it WASN'T coming from an admin but for the most part if you didn't pay attention, you could pull off almost anything.
Such as telling users they have to reboot several times a day because of "issues" their particular computer was having. I had 1 guy reboot about 8-12 times through out the day because his computer was showing violations of its term of use. And rebooting was a 5+ minute ordeal. He would openly complain to those around him (including me) that he wasn't doing anything wrong. This lasted WEEKS before someone spilled the beans about it. Best IT practical joke I ever pulled.