They all log in from the network 129.70.12.x, which appears to be at Bielefeld University, Germany.
Seeing someone logged in from the same network, I asked them if they knew about this but they said they didn't. Maybe it's someone having fun, or maybe we'll see a whole rash of new bots under old names. If you find out anything interesting, mail me.
As always, if you want to know whether you're inviting a bot or a human who's taken a dead bot's name, check the status of the bots on the main FIBS Bots Page.