Found in Vault 106's living quarters, right in front of the locked (average) door south in the local map. It is written by a non-insane vault resident.
I dont know what happened, all of a sudden everyone just started acting strange. The Overseer told us to lock ourselves into our room and wait until security gets the riff raff under control so that's what I'm doing. I managed to catch the security chief on his way past and apparently the weirdos are so out of their head they can't read, so if you're not affected say the word 'Fanzini' and I'll let you in.