There is a lot more to the web than that which immediately meets the eye.
Hidden on the net is online content which is not so easily accessed, known as the Deepnet (also sometimes called Darknet, the Deep Web or Hidden Web).
A part of the Deepnet is accessed through the anonymity network known as Tor.
It may not be surprising to hear that, whilst Tor is used for many legitimate or moral purposes, this part of the internet is also home to a wide range of criminality and illegal content.
Tor is a powerful tool for the well-intended and the nefarious alike.
It simultaneously provides malware authors clever methods for hiding their malicious command-and-control servers from those trying to shut them down, as well as aiding malware analysts in their research.
It is common for malware authors to blacklist traffic from known anti-virus vendor IP addresses, so researchers often use Tor to overcome this.