What is Tor?
Tor, short for The Onion Router, is a free service designed to allow people to browse the web anonymously and to bypass network surveillance. Its goal is to allow individuals and organizations to share information across the Internet without compromising their privacy and anonymity.
Who is Behind Tor?
Tor was originally developed by the U.S. Naval Research Laboratory  for the purpose of protecting government communications. Today it is developed and maintained by the Tor Project, which is also in charge of raising the necessary funds for its development. Tor’s funding comes from donations from sponsors around the world including the U.S. and Swedish governments. Tor’s 2012 financial report  revealed that about 60 percent of its funding came from the U.S. government including 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, it doesn’t mean the Tor Project collaborates with the NSA 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 computers run by volunteers all around the world. These computers are often referred to as “relays”, “nodes” or “routers”. The Tor software is used to build secret pathways through which the traffic travels through the Tor network.
On a public network such as the Internet, traffic is sent directly from the origin to the destination.This not only allows the destination website to track your behavior and know your physical location, but it also allows the “man-in-middle” to know whom you’re talking to and what you’re talking about. In contrast to how Internet traffic normally flows, Tor works differently.
Prior to sending or receiving data, the Tor software first randomly chooses a minimum of three relays to establish a circuit (imagine it as a pathway) to use for data transfer, making sure each relay doesn’t know anything about the entire circuit but only knows which relay it receives data from and which relay it sends data to. One circuit can only be used to transfer data for a certain amount of time (usually 10 minutes). After a circuit expired, a new circuit must be established for later data transfer.
Like layers of onion skins, the data is wrapped into several layers of encryption with each node being able to “peal off” just one layer of encryption. In short, Tor uses a combination of nested encryption and multiple relays to conceal who is sending what.
Who Uses Tor?
Everyday, millions of people around the world use Tor with more than 430,000 connections coming from the U.S. alone . People use Tor for variety of reasons. Normal people use Tor to protect their privacy and personal information from being used or sold without them knowing. People in oppressive countries use Tor to access blocked websites. Law Enforcement, U.S. Government workers, the military, journalists, activists and dissidents use Tor when they need to conceal their communications or have a strong need for anonymity. Unfortunately, the high anonymity and security of the Tor network has also attracted purveyors of illegal sexual content  and criminals who use Tor to sell illegal drugs .
Is Using Tor Legal?
As far as we know, it is lawful to install and use Tor in most countries as long as it’s not being used for illegal purposes. Imagine you have a sharp kitchen knife, a tool you normally use to chop vegetables. If instead you use it as a weapon to harm others, you will likely get arrested and go to jail.
Similar to the above kitchen knife, Tor itself is just a tool, a tool that can be used for both good and bad, a tool that can be used to protect people’s privacy and 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 law enforcement, 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 a in-depth discussion of Tor’s safety, check out this article.)
At least at present, Tor is considered to be safe and is the only practical tool people can use to remain anonymous while online.
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