URL shortening

URL shortening is a technique on the World Wide Web in which a Uniform Resource Locator (URL) may be made substantially shorter in length and still direct to the required page. This is achieved by using an HTTP Redirect on a domain name that is short, which links to the web page that has a long URL. For example, the URL http://en.wikipedia.org/wiki/URL_shortening can be shortened to https://goo.by/GvR7j. This is especially convenient for messaging technologies such as Twitter and Identi.ca, which severely limit the number of characters that may be used in a message. Short URLs allow otherwise long web addresses to be referred to in a tweet. In November 2009, the shortened links on one URL shortening service were accessed 2.1 billion times.^[1]

URL shortening also has problems:

• A long URL contains different parts, which allow a user to judge if the site or url is trustworthy. When shortening an URL this information is lost. The user will be redirected to a site which he or she does not want to visit, and perhaps isn't alllowed to visit.
• Companies who provide url shortening services ar open to attack, like regular sites.When this happens, all the shortened URL may suddenly point to another site, which contains Malware, for example.
• URl shortening is usually offered free of charge. If a provider decides to change its conditions, or goes out of business, all the URLs of this provider will become unusable. As they are shortened, the real domain they pointed to cannot be seen either.
• The sites forwarding the urls can create statistics and profiles on how they are used
• Usenet newsgroups contain messages that will stay up for a very long time. In such contexts, url shorteneing shouldn't be used, as the provider of the shortening service may not be up that long
• There are special sites that allow to check where a shortened url points to, without actually visiting it.
• They can be used by criminals to ask you to install malware for spyware on your computer.^[2]