Image spam bypassing filters

Our Inboxes are being flooded by unsolicited emails because many spam filters are unable to recognise text that has been embedded in an image.

So-called 'image spam', which is often used by peddlers of medications and other types of drugs, isn't a security risk to our home computers as such, but can sometimes be offensive.

A recent image spam campaign, spotted by security firm Sophos, is particularly distasteful, offering a local prostitute-finding service.

"Image spam is often used for promoting things designed to improve your sex life - this latest campaign goes a step further than the usual emails offering drugs and medication," said Graham Cluley, senior technology consultant at Sophos.

"While there's nothing malicious about the emails or the website, the vast majority of computer users will find this type of content totally inappropriate and offensive, and must look to anti-spam solutions if they want such filth eradicated from their inboxes," Cluley said.

Many spam filters work by scanning for certain words or phrases, and can even recognise words that have been deliberately mispelt, with numbers or special characters exchanged for letters.

However, by putting the text onto an image then embedding the image into an email, spammers have a chance of bypassing all but the most up-to-date and sophisticated anti-spam solutions.

"The quantity of image spam in circulation almost doubled in 2006 and is already proving to be one of the biggest spamming trends of 2007 because it's so hard for those anti-spam filters that just rely on analysis of textual spam content to detect it," said Cluley.

http://www.sophos.com/

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