It was around the time people operating on the Internet black market Silk Road started getting arrested that the Tor network landed on the casual observer's radar. It sounded great -- an anonymous way to surf the Internet. But it was already tied up with criminal behavior.
This left many people wondering if using Tor is even legal. And while it may not get you into trouble, it may also not be as good at keeping you out of it as previously believed.
Online, but Out of Sight
For anyone who wants to browse the web anonymously (like citizens under a dictatorship, journalists trying to keep a story secret, undercover police officers, and, yes, criminals), Tor allows you to do just that. From Lifehacker's excellent breakdown:
Tor is short for The Onion Router (thus the logo) and was initially a worldwide network of servers developed with the U.S. Navy that enabled people to browse the internet anonymously. Now, it's a non-profit organization whose main purpose is the research and development of online privacy tools.
The Tor network disguises your identity by moving your traffic across different Tor servers, and encrypting that traffic so it isn't traced back to you. Anyone who tries would see traffic coming from random nodes on the Tor network, rather than your computer.
You May Need an AtTORney
Just using Tor to browse the Internet is not illegal. The download is free, and hiding your IP address and browsing history is not, in and of itself, illegal. However, many of those that use Tor use it specifically for anonymity because they are doing something illegal. And, as recent arrests have proven, it may not be perfect when it comes to hiding a user's identity.
Not only may Tor not keep you hidden from law enforcement, using Tor may actually draw their attention: the NSA and FBI have specifically targeted Tor users in the past. And your ISP may not be thrilled about it either: Comcast has threatened to cut service to customers using Tor.
So feel free to hop on Tor and bask in the freedom of (semi-)anonymous Internet browsing. Just know that if you're breaking the law online, Tor is a lot more like a ski mask than an invisibility cloak.