When I open MSN Messenger, my firewall reports an outbound connection on port 7001 (UDP) by msnmsgr.exe. I have been unable to find out what msnmsgr.exe uses this connection for. MSN Messenger seems to work fine if I block the connection. Does anyone here know what it’s used for?

When you block this does the ad box(on the bottom) in messenger go blank? my first thought is that it is connecting to MSN for the ad box.

The port is a registered port,

afs3-callback 7001/udp callbacks to cache managers

according to here.

The situation as far as I am aware is this:

The callback is needed so you can know when your cached file is updated. The point is that you are absolutely sure when your cache-file is up-to-date. The files are cached locally even when they are not used and they stay in the cache until they get garbage-collected (because of full cache) or until you get a callback.

Although it may appear on the surface that MSN Messanger is working properly with this port blocked, my guess would be that due to the nature of what I have posted above, there IS the possbility that you will have an out of date cache with this program and something COULD go wrong.

I would allow the program to access the port.

No, the advertisement is still there. I think the advertisement uses TCP port 80 HTTP (Hypertext Transfer Protocol).

I used a msn ad killer program on mine cause I found them annoying.

Nope, I don't think the ad is that port, if you bother to read my post.

Building up on the msmsg port subject.
What port does the program use whne connecting to other computer for video and voice chats?

i agree with phantasm i think it is like an updater for msn for ex when a person comes online it updates the cashe.