I've used Windows Messenger service (or, at least, I think that's what it is) before to send a pop-up/broadcast message to all (or selected) users before, but it's been a while. What's the best way ...

Yesterday, for a period of about 2 hours or so, some individual was using the "net send xxx.xxx.xxx.xxx(IP) " through command prompt yesterday, and sending me non-stop messages practically rendering ...