Something strange happened today. I have been using Limewire for years; today my spouse downloaded the software and downloaded some files. We have a cable modem and use a wireless router. I opened Itunes this evening and I had a new icon called Shared and a folder entitled "spouse's name's Limewire Tunes". On her laptop, in Itunes she can see my Limewire files. Is this because we are on the same network? Is there a preference set for this? Thanks!

Yes it's a shared option with both iTunes and LW.
For iTunes, go to edit menu, Preferences -> Sharing & you will see two options.
Look for shared Libraries is what will affect this from LW.
For LW, go to LW's menu bar, Tools > Options > iTunes > Sharing & you will see options there.

The share option is designed for sharing playlists on a LAN. You can disable it from your particular account / computer by turning off Look for shared libraries in iTunes.