As you may have seen on the news recently, there are reports that O2's customer data have been "sold on the dark net". The concept of the "Dark net" or "Dark web" is cropping up more and more, so what is it?
The dark net (or darknet) is just a number of devices set up in such a way that they cannot be traced using normal methods.
To give you an example, assuming you're reading this page with no efforts to mask your online activities, our web server will have recorded the fact that someone at your location has visited this page. While that wouldn't necessarily be immidately clear from the data recorded, with the cooperation with your internet service provider, it would usually be possible to determine where you were when you visited the site. (Incidentally, this is not information that an ISP would provide to just anyone. The point is more that this traceable link exists).
If you were to visit our site using something like Tor, that traceable link between our server and your browser would be broken. When someone connects to another device using Tor, it bounces the connection round the world between many different machines so it's all but impossible for the person at the other end to determine who the other person is and where they are.
On the flip side, with very little effort, it is possible to determine that our website is (as I write this) running on a 1&1 server based in Germany. Therefore, the start and end point of this transaction is known at both ends of the connection.
The purpose of the dark net is to break this link. The point is not to hide the fact that a communication took place, but to hide the start and end point of that communication.
As you would expect, many of those that want to cause trouble on the internet will use this method to hide their tracks. It is often used to hide file sharing, malware and worse.
However, it can and has be used to disguise activities by people living under oppressive regimes in order to get their voices heard by the outside world. Therefore, while the dark net sounds ominous (and it is often used to mask criminal activities), the technology is not inherently evil in itself.