It's a built in messenger for the operating system. It's used on networks for administrators to send messages across the network to users. The problem is that it can be exploited by spyware or even virii / worms to do things like display pop up ads (even when you're not using your web browser). What zoo was saying is that you can disable the service altogether and it won't negatively affect your system or anything.
start -> run -> type services.msc -> look for a service called "messenger" , right click and go to properties -> set startup type to disabled
However "messenger" was not listed in my services.
p.s. The problem is that I installed a anti-virus software today caleed Freedom. And it keeps producing a window telling me the msngr.exe is "potentially" hazardous and wants me to delete it - but I was not sure what it did - or how to do it.
I wouldn't delete the file. Reading up quickly on that antivirus software, it's provided by telus right? It's evidently quite buggy and fubared some people's systems. I'd reccomend something more tried and true like norton antivirus. pm me if you've got an msn account or something.