It may well be searches going on. Check your Library window & shared files & look at the Hits column to the right of the files. This means such shared files have been found in searches.

Other than that, there will probably be some communication going on between your LW & the ultrapeer its connected to. Check your connections window to see what I mean.

If you're concerned about security, then make sure your firewall is up & running (but configured to allow LW) & also you might want to look at this Peerguardian (FREE)