IIRC, this is one
really nasty security hole. It was originally put into Windows so folks in a workgroup could send messages to each other ("Hey, where we going for lunch?" e.g.), but it turns out to be a big time backdoor for folks (hackers) to get into your system when you're on the 'Net. Unfortunately
it's
enabled by default at boot-time (Gee thanks, Microsoft!). It has
nothing to do with so-called "instant messaging" services like AIM (AOL IM), ICQ and similar services available from Yahoo and MSN. I recommend you disable it. Hit your "Start" button, click on "Run," and then type "
services.msc" (without the quotes, of course).
This will give you a huge list of all the "services" that Windows is running, and enable you to select whether you want "auto-start," "run on demand," or "disabled" for each one of them. Another wonderful little gem you'll find in there (and
definitely want disabled) is "
Remote Registry Access" which only allows folks (such as hackers) to remotely get at your registry and (perhaps) totally f**k your computer.
For anyone who's interested, you can PM me and I'll send you a list of 30-odd of these buggers that you can safely disable to make your computer more secure, free up processor time/memory, etc. I hand it out to my students.