There are organisations sponsored by the RIAA, etc. to attempt to stop copyright sharing. These are the organisations responsible for the spam you find on the network. They may also act as a normal user uploading from those who are sharing copyright files such as the most recently released movies and music. That's how they know a person is sharing a particular file.

Is it safe? Not for me to say. After all you are attempting to obtain some copyright files without paying for them. Not all files on Gnutella network are copyright, depends what you are seeking.

I'm guessing you are downloading torrents and not from the gnutella network?