The Wayback Machine (http://archive.org/) is a large archive of web pages, cached since 1997. In simple terms, the Wayback Machine takes “snapshots” of web pages. It uses a spider that finds pages by following links – similar to the spiders used by search engines. If your web page is well-linked from other pages, the Wayback Machine will find it. The Wayback Machine can be blocked from archiving your site through the use of a robots.txt file.