Security firm Symantec has reported a rise in spam messages sent via shortened URLs in its July 2010 MessageLabs Intelligence Report.
Shortened URLs are used in social networks like Facebook and Twitter to exchange URLs between users.
Cyber criminals can use the shortened URLs to inject links to websites that contain spam and malware.
According to the report, the amount of spam spread by shortened URLs had increased over the last year, up from 9.3 per cent to 18 per cent of the total spam circulated at its peak.
Symantec added: "The average volume of spam containing shortened URLs has also increased, with this type of spam appearing in more 0.5 percent of spam on 43 days in the past four months."
Speaking to PC World, Paul Woods, the senior analyst at Symantec's MessageLabs, said: “When spammers include a shortened URL in spam messages, these shortened hyperlinks contain reputable and legitimate domains, making it harder for traditional anti-spam filters to identify the messages as spam.”