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Link rot (or linkrot), also known as link death, link breaking or reference rot, refers to the process by which hyperlinks on individual websites or the Internet in general point to web pages, servers or other resources that have become permanently unavailable. The phrase also describes the effects of failing to update out-of-date web pages that clutter search engine results. A link that does not work any more is called a broken link, dead link, or dangling link. Formally, this is a form of dangling reference: The target of the reference no longer exists. ==Causes== One of the most common reasons for a broken link is that the web page to which it points no longer exists. This frequently results in a 404 error, which indicates that the web server responded but the specific page could not be found. Another type of dead link occurs when the server that hosts the target page stops working or relocates to a new domain name. The browser may return a DNS error or display a site unrelated to the content originally sought. The latter can occur when a domain name lapses and is reregistered by another party. Other reasons for broken links include: * Websites can be restructured, redesigned and/or the underlying technology can be changed, altering or invalidating large numbers of inbound or internal links. * Many news sites keep articles freely accessible for only a short time period, and then move them behind a paywall. This causes a significant loss of supporting links in sites discussing news events and using media sites as references. * Links may expire. * Search results from social media such as Facebook and Tumblr are prone to link rot because of frequent changes in user privacy, the deletion of accounts, search result pointing to a dynamic page that has new results that differ from the cached result, or the deletion of links or photos. * Links can contain ephemeral, user-specific information such as session or login data. Because these are not universally valid, the result can be a broken link. * A link might be broken because of some form of blocking such as content filters or firewalls. * Dead links can also occur on the authoring side, when website content is assembled from Internet sources and deployed without properly verifying the link targets. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「link rot」の詳細全文を読む スポンサード リンク
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