Computer users should think twice before using websites that enable them to shorten URLs.
The warning comes from security supplier Sophos following a hack on URL shortening website Cligs.
An attacker discovered and exploited a security vulnerability on Cligs last night. More than two million URLs were then changed to be directed to a single URL.
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It is not certain what the attacker was trying to gain, but the fact that so many people could be directed to one site could cause massive problems if the site was malicious.
Sophos said URL shortening services like TinyURL, bit.ly and is.gd have increasingly become part of many computer users' everyday lives. Cligs is popular among users of Twitter because they have to condense comments on the microblogging site to no more than 140 characters.
"While Cligs is nowhere near as popular as the likes of TinyURL, it is still used by a substantial number of people, so you can imagine the disruption that can be caused if links no longer go where they are supposed to," said Graham Cluley, senior technology consultant at Sophos.
"While it is not clear what the intentions of the fraudsters were in this case, they could have easily redirected millions of shortened URLs to a website hosting malware," he added.