The Invisible Web: Uncovering Sources Search Engines Can’t See

The paradox of the Invisible Web is that it’s easy to understand why it exists, but it’s very hard to actually define in concrete, specific terms. In a nutshell, the Invisible Web consists of content that’s been excluded from general-purpose search engines and Web directories such as Lycos and LookSmart—and yes, even Google. There’s nothing inherently “invisible” about this content. But since this content is not easily located with the information-seeking tools used by most Web users, it’s effectively invisible because it’s so difficult to find unless you know exactly where to look. In this paper, we define the Invisible Web and delve into the reasons search engines can’t “see” its content. We also discuss the four different “types” of invisibility, ranging from the “opaque” Web which is relatively accessible to the searcher, to the truly invisible Web, which requires specialized finding aids to access effectively.