Introduction
The Deep Web is any Internet content that, for various reasons, cannot be or is not indexed by search engines like Google. This definition thus includes dynamic web pages, blocked sites (like those where you need to answer a CAPTCHA to access), unlinked sites, private sites (like those that require login credentials), non-HTML/contextual/scripted content, and limited-access networks.
Limited-access networks cover sites with domain names that have been registered on Domain Name System (DNS) roots that are not managed by the Internet Corporation for Assigned Names and Numbers (ICANN), like .BIT domains, sites that are running on standard DNS but have non-standard top-level domains, and finally, darknets. Darknets are sites hosted on infrastructure that requires specific software like Tor before it can be accessed. Much of the public interest in the Deep Web lies in the activities that happen inside darknets.
