Webcrawler

A web crawler (also known as a web spider) is a program which browses the web in a methodical, automated manner. Web crawlers are often used to create a copy of all the visited pages for later processing by a search engine, that will index the downloaded pages to provide fast searches. Crawlers can also be used for automating maintenance tasks on a web site, such as checking links or validating HTML code. Also, crawlers can be used to gather specific types of information from web pages, such as harvesting email addresses (usually for spam).