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Peer-to-peer (P2P) file sharing, such as with a software like BitTorrent, has had a resurgence in popularity in recent years. It’s possible you first heard about file sharing in news stories about copyright infringement and lawsuits against companies like Napster or Pirate Bay. While these stories may scare away many users, there are several legal uses for P2P to include sharing large applications and public-domain movies.

If you’re curious to find out what P2P is all about, you’ve come to the right place. In this article, we’ll explain what P2P and BitTorrent are, how they work, and how they can be used legally and safely.

What Is P2P? What Is “BitTorrent?”

Suppose you want to download a particular file — it could be a program, a movie, a book, or even just a word document. How would you typically do that? Most of the time, you go to an app store or a website and just click the download link. This starts the process of transferring the file from the website to your computer.

If you are more familiar with how this process works, you may know that the website is just hosted on another computer (called a web server) somewhere in the world. What you’re really doing is copying the file from that computer to your own — which can take a very, very long time, depending on how fast your internet connection is. If you can use the internet to download files from a web server, you should be able to download files from any internet-connected computer, right?

As it so happens, there is a way to do that. P2P file-sharing was designed as a way for you to safely and reliably transfer files between computers across the internet.

P2P is notably not the only way to transfer files across the internet. You could, for instance, email the file or put it in a shared Dropbox or Google Drive folder. However, neither of those options are practical for transferring large files. These other services are intended primarily for sharing files with a handful of people, whereas P2P is able to share files publicly.

How P2P Works

Every computer on a P2P network is known as a “peer” (also called a “node”). To become a peer in the network, you need to download P2P client software which tells your computer how to connect to the network, how to find files available for download, and how to upload your own files. You may also need to create an account.

There are a couple of terms that you’ll need to know going forward:

  • A leech is a peer that is downloading a file, regardless of whether they are also uploading. In the early days of P2P, it had a much more negative meaning — referring to people that only download a file without also uploading — but that meaning has become less common.
  • A seed is a peer that has the entire file and is uploading it to others.

Every interaction in the network involves a leech downloading a file from another peer (not necessarily a seed, as I’ll explain soon), but it’s actually far more intricate than that. If several seeds are uploading the file that you are trying to download, most modern P2P networks utilize those multiple options to speed up the download process. These P2P networks grab different parts of the file from as many seeds as are practical and allowed by the settings of the network.

With some P2P networks, you can start uploading portions of the file you’ve already downloaded long before you have the full file. Leeches can download that portion of the file if they need it, taking some of the load off the seed computers. This offers a huge overall boost to the network because it acts to further distribute the workload.

By the time your download finishes, you may have downloaded from hundreds of computers and uploaded to hundreds more. At that point, you can choose to either stop sharing or continue to seed the file to other computers. Of course, P2P networks don’t work well when people don’t seed, which is why some networks institute rules to prevent pure leeching. BitTorrent, which we’ll discuss next, uses a rather ingenious solution to that problem.

How BitTorrent Works

BitTorrent networks are very similar to a standard P2P network in most ways. You still download files from your peers and upload those same files to other peers. As with other P2P networks, BitTorrent distributes the workload by allowing downloads to occur from multiple peers at once and by allowing peers to upload those portions before downloading the entire file.

Beyond that, though, the BitTorrent protocol introduces a few advancements that make it different from previous P2P protocols. In particular, BitTorrent introduced an additional server, known as a tracker, and has programmed in a fairness principle called “tit-for-tat.”

The tracker is a central server programmed to help each computer find other computers to download from. In a standard P2P network, finding a computer to download from is a huge bottleneck in the process — your computer basically has to ask around until it finds another computer that knows where to find the file. This is the computer equivalent of finding a job by going door-to-door until you find a “we’re hiring” sign. The tracker’s role is like that of a job board, centralizing all that information so you can find all the available seed and peer computers in a single location.

Tit-for-tat is the way BitTorrent is solving the leeching problem. The more files you upload, the more priority it gives you on the server. The number and speed of your downloads are limited if you aren’t willing to be a giver, as well as a taker. Basically, BitTorrent rewards those who help their peers.

Is P2P Legal and Safe?

Many of us think of the lawsuits around Napster or Limewire when we hear P2P, raising all sorts of questions about the legality of joining and using such a network. Today, many P2P users still use P2P networks to distribute copyrighted content, which is against the law in most countries. P2P file-sharing itself is legal, as long as you only download and upload content for which you have distribution rights.

Malware and viruses are also common concerns with P2P networks. The best way to defend against these problems is to stick to reputable networks. These networks will have protections against malware and viruses at the server level, which is the safest way to avoid these issues. That being said, you should certainly make sure that you are running frequent virus and malware scans on your computer, especially if you do a lot of downloading.

One last concern to keep in mind is privacy. Most P2P software gives you an option of what folders to share when you join the network. The safest method is to pick a single folder that you designate only for storing files you intend to share. Never give the software access to a folder that contains (directly or in a subfolder) personal or private files or anything that you don’t have distribution rights for. Remember that any user on the network can get access to any file that is in your shared folder.

Can P2P Be Traced?

It absolutely can. You might assume you are safe since you are behind an anonymous username and nobody sees your real name, address, or any kind of contact information. However, there’s one critical piece of information that the network uses to initiate the process: your IP address.

It isn’t difficult for any nefarious actor or legal entity to make use of this single piece of information to track the digital and non-digital you. The Motion Picture Association (or MPAA), in particular, has been known to use IP tracking to catch the sharing of copyrighted material.

If you want to avoid making your IP address known to the P2P network, you need to use a VPN, which will assign you a proxy IP address. This proxy address is seen by the P2P network instead of your own, and a good VPN prevents the tracing of that proxy address back to your own IP. This is the best way to maintain privacy while using a P2P or BitTorrent network.


Which BitTorrent Client Is Best?

For most users, BitTorrent is a great place to start your P2P file-sharing experience. To do that, you’re going to need a BitTorrent client, so here are a few options that are ideal for beginners.

  • qBittorrent — qBittorrent is a fast and simple BitTorrent client with no ads. Its simplicity comes at the cost of customizability, though, so advanced users might want to look elsewhere.
  • Vuze — Vuze offers an experience that starts off simple but has a lot of customization available if you choose to use it. You will have to deal with ads, though.
  • uTorrent — uTorrent is the most popular BitTorrent client everywhere except China, partially because it is maintained by the developers of BitTorrent. However, some users have shifted away because of their use of ads and a few high-profile security issues in recent years.

Time to Share

P2P file sharing opens up a whole new world of opportunity for internet users. Sadly, the real usefulness of these networks has been overshadowed by their use in illegal activities like copyright infringement.

If you want to dive right in with some legal downloads of music, movies, and more, check out this list of legal torrent sites. You’d be amazed how many older or B-tier movies have made their way into the public domain. These movies are a great way to make your media center PC really stand out. You won’t find many of these movies on Netflix or HBO, so BitTorrent may be your best chance to see them.