Incidents of shortened URLs in spam messages have skyrocketed since the start of this week.
Email filtering service MessageLabs reports that more than 2.25 per cent of junk mail messages feature spamvertised links laundered through URL redirection services.
URL redirection services map between lengthy web addresses and shortened URLs. Such services are a vital adjunct to services such as Twitter, which restricts users to a 140 character message limit.
Spammers have begun using these URL shortening services because they help to disguise the true destination of promoted links, a factor which might go on to play a part in drive-by download malware attacks as well as already observed incidents of spam-promoted websites. URL redirection services require no registration, making their services more attractive for legitimate users and spammers alike.
"Donbot, the botnet responsible for sending approximately five billion spam messages every day, is one of the main culprits for using this technique," said Paul Wood, MessageLabs Intelligence senior analyst at Symantec. "Links of any size all need to be treated with caution."
The security of URL shortening services was among the first issue put under the microscope by the Month of Twitter Bugs project. The security awareness raising exercise debuted on 1 July with an advisory on four cross-site scripting (XSS) vulnerabilities in the bit.ly URL-shrinking service.
Three of the flaws had already been plugged before the advisory, while the remaining vulnerability was fixed on the same day as the bulletin. ®