The "clear" web is the section of the Internet that can be accessed from any browser and is regularly crawled and indexed by search engines including Google, Yahoo, and Bing. The "deep" web is an unindexed area. The "dark" web is a small section of the deep Internet often associated with illegal activity.
Those exploring the deep web will come across .onion website domains. The .onion address is a hat tip to onion routing, an anonymizing technique used by Tor to mask the digital footprint of users.
.onion addresses are offered by all manner of companies, services, and individuals, ranging from Facebook to media outlets and scientific research resources.
The core reasons are privacy and, to an extent, anonymity. It is far from just those interested in criminal pursuits that appreciate privacy; activists, the media, those living in countries heavily invested in censorship, whistleblowers, as well as members of the general public that take their personal data, tracking, and information seriously all use the service.
The deep web is as varied as the standard Internet and you can find anything from the .onion alternatives of popular service such as media publications, secure drops for whistleblowers, historical content, and simple, mundane blogs. Facebook, too, offers a .onion address as an alternative for countries which actively block the social network.
It might be slower to browse due to the need for the Tor network, but it is more secure and private.
Also known as the darknet, this sector of the web is linked to marketplaces, some of which sell illegal drugs, weaponry, cheap gadgets, stolen data dumps, counterfeit money and documents. Websites and forums which host illegal content such as child pornography are also present.
However, there are also thousands of dead links and uninteresting pages, and only a tiny percentage of websites relate to illegal sales or extreme content.
It is not illegal in itself to browse the dark web, on the condition you are not actively seeking websites that host highly illegal content, such as child pornography.
Anyone who believes they are safe from law enforcement by trading in the dark web is incorrect, as theclosure of Silk Road has shown. The use of virtual currency and the Tor browser does not guarantee anonymity, and purchases most often are delivered through traditional means.
Another element to be aware of in marketplaces is the vast array of scams. If you take a risk on a purchase, no matter what it is, you have no guarantee.
Exit scams are common, honeypots exist, and, unlike regulated sources, you cannot file for a refund should you lose your money.
There are many myths and legends surrounding the deeper parts of the Internet, such as the existence of red rooms and Mariana's Web, and many of which are yet to be proved or are simply nonsense.
However, in the same breath, there are depraved websites which display some of the most heinous and vile aspects of humanity and what we are capable of.
International law enforcement works hard to bring down the worst of the worst, but there are some places you simply won't want to stumble upon.
Keep in mind, it is not just the dark web which has illegal goods for sale and horrific content available -- it is rife on the surface, too. Common sense should be king no matter where you browse.