More warnings have been issued over the spread of image-based spam, through which pictures are used to lure victims into downloading spyware or falling for scams.

While it seems surprising, to say the least, that supposedly best-in-breed filtering software is still being bypassed by image-based emails, Computer Weekly reports that attackers are increasingly using them to beat existing controls.

According to security firm CipherTrust, image spam now accounts for 15% of all unsolicited traffic, and is mostly used in stock scams where victims are used to ramp shares in little known firms.

“These are Pink Sheet stocks, traded on the OTC bulletin boards, that typically don’t get a lot of volume,” said Dmitri Allperovitch, a research engineer at the firm.

“They’re niche companies with no profit and no products, so when you see a spike from almost no trades to two or three million when the spam is sent out, you know there were a lot of people who fell for it.”