What is Tor?
Tor, short for The Onion Router, is a free service designed to allow people to browse the web anonymously, and to evade all known methods of surveillance. Tor’s purpose is to allow individuals and organizations to view and exchange information across the Internet without compromising their privacy or anonymity. Information transmitted using Tor is extremely secure and highly anonymous, which is why many governments and private organizations use it.
Who is Behind Tor?
Tor was originally developed by the U.S. Naval Research Laboratory  for the purpose of protecting sensitive government communications. Today it is developed and maintained by the Tor Project, which is also in charge of raising the funds necessary for its ongoing development. Tor’s funding comes from donations by sponsors from around the world, including the American and Swedish governments. Tor’s 2012 financial report  revealed that about 60 percent of its funding came from the U.S. Department of Defense, the parent agency of the NSA. It is important to note that even though the U.S. government contributes a large percentage of funding for the Tor Project, that doesn’t necessarily mean the Tor Project collaborates with the notorious NSA surveillance programs in any way.
How Tor Works
Tor consists of two parts: the Tor network, and the (free) Tor software. The Tor network is comprised of more than 5,000 computers run by volunteers from all around the world. These computers are referred to as “relays”, “nodes”, or “routers”. The Tor software is designed to send encrypted network traffic across untraceable pathways determined by the computers that govern the worldwide Tor network. The Tor software, working in concert with the computers acting as network routers, ensures that the Tor network is extremely difficult to compromise, and therefore, highly secure.
On a public network (such as the Internet) traffic is sent from the origin to the destination by an easily traceable route.This not only allows the destination website to trace your physical location, it also allows the “man-in-the-middle” – a well known method of attack – to intercept your message and see who you’re talking to and what you’re saying. Intercepting messages sent across a public network is not difficult at all. In contrast to how normal Internet traffic flows, Tor is far, far more secure.
Prior to sending or receiving data, the Tor software first randomly chooses a minimum of three relay points to establish a unique and untraceable route (imagine it as a pathway) for each data transfer, making sure every relay knows nothing about the entire route, but only knows which relay it receives data from and which relay it sends data to. Each “route” can be used to transfer data for a limited amount of time (usually 10 minutes). When a route expires, a new route must be established for subsequent data transfer. This process makes it virtually impossible to observe, predict, trace, record, or follow the pathway any piece of data (packet) travels en route to its intended recipient.
Like the layers of an onion, each packet of data is wrapped in several layers of encryption with each node being able to peel off just one layer at a time. In short, Tor uses a combination of nested encryption and multiple relays to conceal who is sending what to where, ensuring that even the most determined hacker is confronted by an impossibly difficult ‘puzzle’, where finding all the pieces just isn’t feasible. That is the brilliance of Tor. Even so, you must understand that no system of communication, nor any system of security, is utterly impregnable. In order for Tor to work ‘as advertised’ you must ensure that you use it correctly.
Who Uses Tor, and Why?
Millions of people around the world use Tor regularly, with more than 430,000 daily connections coming from the U.S. alone . People use Tor for a variety of reasons. Average citizens use Tor to protect their anonymity and prevent personal information from being used or sold without their permission, which is entirely legitimate, and legal. Also, law enforcement agencies, many governments and military branches, journalists, activists and dissidents, and many business people use Tor when they wish to remain anonymous or protect their communications, data, etc. Unfortunately, the Tor network has also attracted purveyors of illegal content  and other criminals who use Tor to sell drugs, weapons, and other contraband materials .
Is Using Tor Legal?
Yes, using Tor is legal in most countries, provided you are not deploying it to conceal criminal activities. Privacy and anonymity are not criminal pursuits, except where certain totalitarian regimes hold power. Citizens of most countries can use Tor without concern of being prosecuted, however, be advised that the NSA does keep a close eye on who uses Tor, for reasons both obvious and obscure. But, those who use Tor for legitimate and legal reasons have little to fear.
Imagine you have a sharp kitchen knife – a tool you normally use to prepare foods – if instead you use it as a weapon to harm others, you will in most cases go to jail. Like your kitchen knife, Tor is a tool that can be used for both good or bad, and can obviously be used to commit crimes. Criminals who think they can use Tor to conduct illegal activities and get away with it will eventually get busted by the authorities, often a lot sooner than they think.
How Safe is Tor?
Recent research  showed that, theoretically, it is possible to de-anonymize the Tor network and reveal the true identities of certain Tor users. However, it is technically difficult or impractical to build a working system can effectively de-anonymize Tor based on these theories. (For an in-depth discussion of Tor’s safety, check out this article.)
At present Tor is considered to be safe and is the only practical tool people can use to remain completely anonymous while online.
Can I use BitTorrent with Tor?
No. BitTorrent and other file sharing services are generally blocked by the Tor network. Even if you manage to get them working together, the speed will be extremely slow since data will be encrypted, unencrypted, and re-encrypted multiple times when passing through the network. This makes Tor impractical as a BitTorrent transport.
It’s Not “TOR” But “Tor”
The correct spelling of Tor is “Tor,” only the first letter is in uppercase.
 Tor Project: Financial Reports
 Tor Metrics Portal: Users
 Tor users compromised in child porn takedown