P2P or peer to peer file sharing programs are software programs that people use to share files with others on the Internet. The more popular ones are Limewire, Kazaa and Bittorrent, however there are dozens of them in various flavors available for free on the Internet.
What these programs do is give the user access to millions of files shared by people from their computers via the Internet. Many people use these programs to download music, movies and software programs. However, there is also a wide variety of porn available via these networks, including child porn.
Since the purpose of these programs is file sharing, they can open the user's computer up to the Internet for that purpose.
According to the Electronic Communications Act:
(g) It shall not be unlawful under this chapter or chapter 121of this title for any person - (i) to intercept or access an electronic communication made through an electronic communication system that is configured so that such electronic communication is readily accessible to the general public;
Sounds like your computer meets this requirement if you are sharing files with other people on the Internet doesn't it?
The reason I mention this, other than the obvious, is that I worked on a child porn case a couple of years ago where law enforcement, while watching the files pass over the Gnutella network, (Gnutella is the network that many of these programs use for transmitting files.) spotted some CP files. Since the IP address and location of the receiving computer is shown to them, they were able to identify a computer in the local jurisdiction.
They then confirmed that the computer was open for sharing, so they connected to the computer and looked at the hard drive. (See the ECA excerpt above.)
They were able to confirm that CP files resided on the computer hard drive, so they then issued a subpoena to the Internet service provider (ISP) for the computer and obtained the subscriber's name and address.
They obtained a search warrant for the premises and computer and subsequently arrested two people.
Unsophisticated users of these sharing programs rarely realize that any file listed can actually be contraband. Just because it says it is one thing in the description, you have no idea what you are really downloading until it is flowing to your computer.
And that can get you in some serious trouble.
Especially if law enforcement happens to be monitoring traffic at that time and decides to pursue a case against you.
Also, you don't have to be sharing these files to get into trouble with the law since possession alone is enough to be arrested and possibly convicted.
However, if your computer is open to sharing, then the charges can escalate beyond possession to purveying and that is serious business.
Defending these cases can be complex and requires a broad knowledge of file sharing software and other software that I won't mention here since I don't want to give away any secrets.
My advice to people who ask me: Don't use these programs at all.