The internet is a much, much bigger place than you probably realise. You know about Facebook, Google, Netflix and Amazon and maybe the millions of other websites that you can access from your usual web browser.
But there's more: the Dark Web and the Deep Web loom in much shadier corners. You won't see any of this stuff in the results when you do a Google search, so what exactly can be found on these dangerous sounding places? Should you even want to visit the Dark Web or the Deep Web?
Here's what you need to know.
What is the Dark Web?
The Dark Web refers specifically to websites that exist behind multiple layers of encryption and cannot be found by using traditional search engines or visited by using traditional web browsers.
Almost all sites on the so-called Dark Web hide their identity using the Tor encryption tool. You may know Tor for its ability to hide your identity and activity. You can use Tor to spoof your location so it appears you're in a different country to where you're really located, just like when you use a VPN service.
When a website is run through Tor it has much the same effect.
Indeed, it multiplies the effect. To visit a site on the Dark Web that is using Tor encryption, you have to use Tor. Just as your IP address is bounced through several layers of encryption to appear to be at another IP address on the Tor network, so is that of the website.
Put simply, there's a lot more secrecy than the already secret act of using Tor to visit a website on the open internet - for both parties.
Thus, sites on the Dark Web can be visited by anyone, but it is very difficult to work out who is behind the sites. And it can be dangerous if you slip up and your identity is discovered.
You can also read our in-depth guide to using Tor if you want to know more about using the web anonymously and sending messages securely.
What's on the Dark Web?
Not all Dark Web sites use Tor. Some use similar services such as I2P, for example the Silk Road Reloaded. But the principle remains the same. The visitor has to use the same encryption tool as the site and - crucially - know where to find the site, in order to type in the URL and visit.
Infamous examples of Dark Web sites include the Silk Road and its offspring, such as Dream Market. The Silk Road was a website for the buying and selling of recreational drugs, and a lot more scary things besides. But there are also legitimate uses for the Dark Web.
People operating within closed, totalitarian societies can use the Dark Web to communicate with the outside world. And given recent revelations about US- and UK government snooping on web use, you may feel it is sensible to take your communication on to the Dark Web.
The Dark Web hit the headlines in August 2015 (and many times since) after it was reported that 10GB of data stolen from Ashley Madison, a site designed to enable bored spouses to cheat on their partners, was dumped on to the Dark Web.
Hackers stole the data and threatened to upload it to the web if the site did not close down, and they eventually acted on that threat. The spouses of Ashley Madison users received blackmail letters demanding they pay $2500 in Bitcoin or have the infidelity exposed.
In March 2015 the UK government launched a dedicated cybercrime unit to tackle the Dark Web, with a particular focus on cracking down on serious crime rings and child pornography. The National Crime Agency (NCA) and UK intelligence outfit GCHQ are together creating the Joint Operations Cell (JOC).
Dark Web vs Deep Web
Although all of these terms tend to be used interchangeably, they don't refer to exactly the same thing. An element of nuance is required. The Deep Web refers to all web pages that search engines cannot find.
Thus the 'Deep Web' includes the 'Dark Web', but also includes all user databases, webmail pages, registration-required web forums, and pages behind paywalls. There are huge numbers of such pages, and most exist for mundane reasons.
For example we have a 'staging' version of this very website that is blocked from being indexed by search engines, so we can check stories before we set them live. Thus for every page publicly available on Tech Advisor (and there are literally millions), there is another on the Deep Web.
The content management system into which I am typing this article is on the Deep Web. So that is another page for every page that is on the live site. Meanwhile our company intranet is hidden from search engines, and requires a password. You can browse to it if you know the URL, but it won't appear in a Google search.
Use an online bank account? The password-protected bits are on the Deep Web. And when you consider how many pages just one Gmail account will create, you understand the sheer size of the Deep Web.
This scale is why newspapers and mainstream news outlets regularly trot out scare stories about '90 percent of the internet' consisting of the Dark Web. They are confusing the generally dodgy Dark Web with the much bigger and generally more benign Deep Web.
What is the Dark Internet?
Confusingly, 'Dark Internet' is also a term sometimes used to describe further examples of networks, databases or even websites that cannot be reached over the internet. In this case either for technical reasons, or because the properties contain niche information that few people will want, or in some cases because the data is private.
A basic rule of thumb is that while the phrases 'Dark Web' or 'Deep Web' are typically used by tabloid newspapers to refer to dangerous secret online worlds, the 'Dark Internet' is a boring place where scientists store raw data for research.
How to access the Dark Web
Technically, this is not a difficult process. And it is not illegal to browse the Dark Web. You simply need to install and use Tor. Go to www.torproject.org and download the Tor Browser Bundle, which contains all the required tools. Run the downloaded file, choose an extraction location, then open the folder and click Start Tor Browser. That's it.
The Vidalia Control Panel will automatically handle the randomised network setup and, when Tor is ready, the browser will open; just close it again to disconnect from the network.
Depending on what you intend to do on the Dark Web, some users recommend placing tape over your laptop's webcam to prevent prying eyes watching you. A tinfoil hat is also an option. If you're reading in the hope of finding out about torrent files, check out our separate guide on how to use torrent sites in the UK.
The difficult thing is knowing where to look on the Dark Web. And since most Dark Web sites are used for illegal purposes I am not going to offer any recommendations. It is at this point l leave you to your own devices and wish you good luck and safe surfing.
A warning before you go any further: once you get into the Dark Web, you *will* be able to access those sites to which the tabloids refer. This means that you could be a click away from sites selling drugs and guns, and - frankly - even worse things. Plus, there's a whole host of malware which can cause havoc to your device and data, so there are certainly risks.
Aggregation sites such as Reddit offer lists of links, as do several Wikis, including http://thehiddenwiki.org/ - a list that offers access to some very bad places. Have a quick look by all means, but please don't take our linking to it as an endorsement. It really isn't.
Also, Dark Web sites do go down from time to time, due to their dark nature. But if you want good customer service, stay out of the dark!
And do heed our warning: this article is intended as a guide to what is the Dark Web - not an endorsement or encouragement for you to start behaving in illegal or immoral behaviour.