Explorer Sending Unnecessary Packets

I have this problem where everytime I right click on a file (not folders or drives or desktop icons - just files) to bring up the context menu, or try to open a file by double clicking, explorer starts communicating with another machine on the network (another user - not a switch or a router) through TCP port 139.

Is there any reason why this would happen and how can I stop it? It is causing explorer to hang for about 15 seconds, since he is blocking every IP on the network. I have used ad-aware and norton very recently with very recently updated vrius definitions.

 

port 139 is assigned to netbios-ssn. You can look that up as www.iana.org. A search on Yahoo brings up some interesting articles that I suggest you have look at.