Converting a long URL name into a short one. Also called "URL redirecting," there are many free URL shortening services on the Web that take a long URL, convert it to a short name and perform the redirection for the user when the short URL is clicked. URL shortening can be used when sending extremely long URLs in e-mail messages or chat rooms, because the URL is often broken up by the time it reaches its destination. The single string of characters is turned into multiple lines and no longer serves as a clickable link.
Although the recipient can patch the URL back together by copying and pasting the lines into the browser's address field, a short URL eliminates the problem in the first place.
There are at least two completely different security issues involved in using the short URL functionality.
Vulnerabilities by the short URL providers
This is the most serious security issue.If the system itself is somehow compromised, the consequences may be severe. An insider within the short URL provider or an external hacker may change the system in such a way that the short URLs do not "translate" to what the users intended. Instead the short URLs could transfer the innocent surfer who clicks on a short URL to web sites with malicious content (worst case).
And this scenario is not just theoretical:
15 June 2009 one of the URL shortening services - Cligs - was hacked according to a blog posting on the provider's web site. This affected around 2 million short URLs, which after the hacking linked to another destination than intended.
Security issues caused by malicious users of the system
This type of issues is possible if (as!) not all users of such a system may be benignant. Although the short URL providers may have some system in place to check the web pages that the short URLs refer to, such systems are never foolproof. The creators of a short URL may refer this to e.g. a malicious web site, or to a site where she receives some profit based on the number of visitors coming from a particular URL.
Use Trusted Secure Short URL Services
McAf.ee | goo.gl
McAf.ee | goo.gl
McAfee Secure URL Short sites http://mcaf.ee/ help keep you safe from identity theft, credit card fraud, spyware, spam, viruses and online scams.
After Shortening: http://mcaf.ee/ba67d
Google URL Shortener at goo.gl is used by Google products to create short URLs that can be easily shared, tweeted, or emailed to friends
Before Shortening: http://simplygetit.blogspot.com/
After Shortening: http://goo.gl/Zq3NV