Stegano is a malware toolkit that allows users to hide malicious code in images. The kit’s name comes from steganography, which is a method of encoding secret data within a file for subsequent decoding.
In late 2016, Stegano was used in a malvertisement campaign that placed malicious code in PNG images in banner ads on prominent websites. The perpetrators hid their scripts within the code for transparency parameters in some pixels within images. The appearance of the images were altered slightly but not to the extent that the difference would be noted by a casual viewer. The attackers then used the image in an ad and bought display spots on popular websites. ESET, the IT security company that reported the exploit, has not disclosed the names of the websites affected, since the sites themselves were not at fault.
Depending on undisclosed user profile variables, site visitors were either served a clean ad or a malicious one that enabled remote installation of malware on the users’ computers. The attack targeted users of Internet Explorer and exploited vulnerabilities in some versions of Flash Player. Malware installation was automatic and did not require that the user click the ad. Researchers reported that there were two ads in the campaign, one purportedly for privacy software called “Browser Defence” and one for an image-capturing product called “Broxu.”
According to ESET the malicious ads had installed various malware to the computers of over a million users within the preceding two months. Robert Lipovsky, a senior malware researcher with the company, said that figure was a conservative estimate.
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- Readers of popular websites targeted by stealthy Stegano exploit kit hiding in pixels of malicious ads