|This page in a nutshell: Steps may be taken to reduce or repair dead external links.|
Like most large websites, Wikipedia suffers from the phenomenon known as link rot, where external links become dead, as the linked web pages or complete websites disappear, change their content, or move without HTML redirection. This presents a significant threat to Wikipedia's reliability policy and its source citation guideline.
In general, do not delete cited information solely because the URL to the source does not work any longer. Tools, procedures, and processes are available as outlined in this document.