DOS Messaging Question - Related To UNIX Process Problem

This is a strange request.

I know there is some sort of crude DOS tool that allows you to communicate to another PC either using its IP adress or PC name. But I can’t remember where aor what its called, any ideas?

Reason for asking here, Someone has telnet’d on a UNIX server I have my app on and has kicked of a MASSIVE task that is going mess with my data cunching. I can identify the pst he’s come in on and get the IP address (from which nslookup gives me the PC name). I need to get in touch but I don’t know who it is due to generic login addresses.

Any help appreciated.
Neil