The "Hidden Internet," sometimes called the "Deep Web" or the "Invisible Web," has been estimated to be 500 times larger than the indexable Web (Michael K. Bergman, "The Deep Web: Surfacing Hidden Value").

Why are so many Web pages hidden?

• Intranets and other protected areas with password restrictions.
• Subscription databases requiring passwords.
• Database technology that precludes page-level indexing.
• Sites that generate "on-the-fly" Web pages in response to user input.
• Non-textual repositories (satellite imagery, sound files, video files).

Some examples of Hidden Internet sites

• The Library Catalog
• Congress.gov
• Hollis: Harvard University Library Catalog
• Handbook of Latin American Studies
• National Criminal Justice Reference Service Abstracts Database
• TopoZone (topographic maps)
• Interactive Global Geostationary Weather Satellite Images
• The Sceptic's Dictionary
• Jeffrey's Japanese<->English Dictionary Server

  Keep in mind that most of the databases in the University Libraries Databases section are hidden Internet resources, since they require a password for access. The library provides easy access to the DU community through our proxy system.