A search engine cache is a cache of web pages that shows the page as it was when it was indexed by a web crawler. Cached versions of web pages can be used to view the contents of a page when the live version cannot be reached, has been altered or taken down. A web crawler collects the contents of a web page, which is then indexed by a web search engine. The search engine might make the copy accessible to users. Web crawlers that obey restrictions in robots.txt or meta tags by the site webmaster may not make a cached copy available to search engine users if instructed not to. Search engine cache can be used for crime investigation, legal proceedings and journalism. Examples of search engines that offer their users cached versions of web pages are Bing, Yandex Search, and Baidu. Search engine cache may not be fully protected by the usual laws that protect technology providers from copyright infringement claims.