Cracked CAPTCHAs used to create malicious blogs
Blogs on Google's blogging system redirect to spam sites.
Spammers are using botnets to
mass-create phony blogs on Google's free Blogger system, with the phony entries redirecting to spam sites.
According to research by security company
Websense, a large botnet is used to surpass the CAPTCHAs used by Google
in an attempt to prevent automatic registration of blogs. As seen in similar
cases, the success rate of cracking the CAPTCHA is relatively low (in this case it is believed to be between 8 and 13
per cent), but still high enough for a large botnet to create a significant number of blogs.
Since many spam filters block emails that contain links to sites that are known to
spam and/or serve malware, spammers have started to use tricks to hide the URL. One such trick
is the use of Google's "I'm feeling lucking" button, together with a cleverly constructed search, while
recently an open redirect in Google's AdSense has been used to trick spam filters into
believing a URL is harmless.
By making use of the facility in Blogger to have a blog redirect to an entirely different website,
spammers have managed to obtain a large number URLs on the blogspot.com domain that redirect to their
sites. Such URLs occur in many genuine emails and there is no way for a spam filter to decide whether such
a URL links to a real blog, other than by following the link and studying the actual website.
Details of the Websense researchers' findings are here.
25 April 2008
Tags:
blogger, captcha, spam.
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