More than 2.2% of spam contains shortened URLs.
URL shortening services have proven recently to be popular not just among microbloggers in need of shorter URLs, but also among spammers attempting to disguise the websites they are spamming. According to email filtering service
MessageLabs
, well over 2 per cent of current spam contains a shortened URL.
URL shorteners such as
tinyurl.com
and
bit.ly
have been around for over a decade but have become very popular recently among users of microblogging sites such as
Twitter
(which restrict users’ entries to a maxiumum number of characters – 140 in the case of
Twitter
).
Because most of these services are free and require neither registration nor CAPTCHA solving, they can be used to automatically generate innocent-looking URLs that redirect to websites containing malware and/or spamvertised products. While it is possible for spam filters to follow the URLs, this requires significantly more resources than being able to look up the URL against an existing blacklist. Furthermore, end-users are more likely to click on such links because their malicious or otherwise questionable nature is disguised in the shortening process.
End-users are advised to exercise caution when clicking on any shortened URLs, while the URL shortening services face a tough task in finding a way to prevent their systems from being abused by spammers.
Posted on 09 July 2009 by
Virus Bulletin
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