msn messenger service 2.2 came from?

where does msn messenger service 2.2 came from? is it from the OS installation? IE installaton? we are presently isolating this problem and we can’t find out where it does came… some of our workstations here does have MSN MESSENGER SERVICE 2.2 installed when you view the add remove programs…. and some don’t have but with the same OS and IE version, same standard installation. not knowing where it came from, the users didn’t installed it, pls help… thanks!!!