I don't understand how searching for known CP files on Gnutella is an illegal search. It could be a lack of technical understanding on my part, but I thought of it like this:
There's an officer looking for users of the new getuhigh drug. If the officer stops everyone to search them for getuhigh, I understand that that's an illegal search. If the officer stops and searches only those people who are yelling out to the general public "want to buy some getuhigh?, I've got some right here," then that wouldn't seem like an illegal search.
Now suppose there's an officer looking for CP on the Gnutella file sharing network. Let's say the officer has a special program, hackunow. If the officer uses hackunow to search the entire computer (not just the shared files) of everyone on Gnutella, I could see that as an illegal search. If the officer searches Gnutella for publicly shared files called herestheCPrighthere.jpg and only then uses hackunow on the specific users sharing those files, that wouldn't seem like an illegal search because those users are publicly announcing that they have CP. If the file has a more generic name ( hereitis.jpg ), then that might be too generic to justify use of hackunow, but wantsomeCPherecomegetit.jpg wouldn't seem to be generic.
I don't understand anything beyond the basic idea of Gnutella as a file sharing network, but don't you have to place whatever you want to share in a folder or specifically tell Gnutella to share a particular list of files? I don't understand how that wouldn't be equivalent to yelling out "here's the CP," "gethuhigh for sale here," etc..