The use of truncated URLs is becoming an increasing security risk as spammers and malware writers are using the shortened URLs to hide malicious content.
This new trend has been see as spam increases through Twitter and now has shown up in e-mail spam too. The problem is that not every spam/virus protection suite available can drill down to the original URL. This means that people are more likely to click on a URL that has been shortened.
The use of truncated or shortened URLs became popular with Twitter as it allows someone to "tweet" a long URL without exceeding their 140 character limit.
This new shift will follow with an increase in exposure to Malware for many users as Companies like Symantec, ESET, McAffee, and others race to catch up.