Microsoft's InstantMessenger software.  Similar but not identical to ''MSN Messenger'' and ''.NET Messenger''.  Bundled with WindowsXp, and related products available for free download for other Microsoft operating systems and MacOs.

See http://messenger.microsoft.com/

Windows Messenger uses the DotNetPassport system for user identification.

FAQ: http://www.microsoft.com/WindowsXP/pro/techinfo/administration/rtcfaq/default.asp

----

You can't uninstall WindowsMessenger from WindowsXp.  Well, you're not supposed to be able to, at least.  C:\WINDOWS\INF\SYSOC.INF, globally replace HIDE with nothing, and you can magically uninstall quite a few things.

It's not so much the bundling that bothers me as MicroSoft forcing you to have a component on your system...