URL shorteners have been around for quite some time. One of the first to rise in popularity was TinyURL.com. Say you have a nice long link like this:
http://rover.ebay.com/rover/1/711-53200-19255-0/1?t ype=3&campid=5336224516&toolid=10001&customid=tiny- hp&ext=unicycle&satitle=unicycle
Services such as TinyURL will turn that link into this:
It works by creating a redirect to your original link. With services such as Twitter that restrict to 140 characters, URL shorteners have exploded in popularity. Bit.ly evens takes this a step further by offering real-time link tracking services. However, there are some things to consider when using these services.
Recently, a hacker hijacked Cligs, another URL shortener service, where more than two million URLs were changed to be directed to a single URL on another site. While this example was not malicious, you can see the potential security issues and vulnerabilities. You now have a middleman who controls all of your links, not you. What happens if the service is down? Or the company that runs the service shuts down? There is a nice article entitled "Why You Shouldn't Rely On URL Shorteners" that talks about these issues.