redirection services are often themselves added to spam blocklists. Another privacy problem is that many services' shortened URL format is small enough that it is vulnerable to brute-force search. Many people use URL shorteners when they share links to private content, and in fact many web services like Google Maps have offered automatic generation of shortened links for driving directions that reveal personal information like home addresses and sensitive destinations like "clinics for specific diseases (including cancer and mental diseases), addiction treatment centers, abortion providers, correctional and juvenile detention facilities, payday and car-title lenders, gentlemen’s clubs, etc." Additional layer of complexity Short URLs, although making it easier to access what might otherwise be a very long URL or user-space on an ISP server, add an additional layer of complexity to the process of retrieving web pages. Every access requires more requests (at least one more DNS lookup, though it may be cached, and one more HTTP/HTTPS request), thereby increasing latency, the time taken to access the page, and also the risk of failure, since the shortening service may become unavailable. Another operational limitation of URL shortening services is that browsers do not resend POST bodies when a redirect is encountered. This can be overcome by making the service a reverse proxy, or by elaborate schemes involving cookies and buffered POST bodies, but such techniques present security and scaling challenges, and are therefore not used on extranets or Internet-scale services. Notable services Open source and commercial scripts are also available for redirecting and shortening links, usually written in PHP as a web application or a plugin for one of the popular applications such as WordPress. Such scripts avoid many issues with shortening services, keep the domain name as part of the shortened link, and can be made private. See also Country code top-level domain Domain Name System Emoji domain Generic top-level domain Link rot List of Internet top-level domains Semantic URL Vanity domain References External links Comparison of URL Shortening Services, SearchEngineLand. April 2009. URL Internet terminology URL-shortening services