A p2p network is a filesharing community. For example Kazaa has movies, music, software, anything and everything you can think of. The problem is more times than not these files were never intended to be shared. They are pirated. Many people use these networks to try to avoid buying whatever software or music etc that they need. You also run into getting bad downloads ie incomplete files, choppy music, virus and trojans, just to name a few examples. Software is required to transfer these files and many times this software is infected by spyware/adware. With anything they have their pros and cons.