Researchers detected 191,970 bad ads and estimates that around 1 million users were impacted.
A massive adware campaign has so far impacted up to a million Mac users, using a tricky steganography technique to hide malware in image files.
Researchers at Confiant and Malwarebytes said the attacks have been running since Jan. 11, using ads on the web and
steganography to spread; steganography being the practice of concealing secret messages, code or information within otherwise innocuous-looking text or images. The tactic has been used in several campaigns over the past year, including in
uploaded images on trusted Google sites and even in
memes on Twitter.
In the Mac campaign, a victim first comes across an ad harboring an image – however, in reality, JavaScript malware is hiding within the image-file code in the ad. Once clicked, the malicious ad infects the Mac user with the Shlayer trojan, which masquerades as a Flash upgrade and in turn redirects the victim to an adware installer.
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