Millions of people visiting mainstream websites over the past two months have been exposed to a novel form of malicious ads that embed attack code in individual pixels of the banners.
Researchers from antivirus provider Eset said “Stegano,” as they’ve dubbed the campaign, dates back to 2014. Beginning in early October, its unusually stealthy operators scored a major coup by getting the ads displayed on a variety of unnamed reputable news sites, each with millions of daily visitors. Borrowing from the word steganography—the practice of concealing secret messages inside a larger document that dates back to at least 440 BC—Stegano hides parts of its malicious code in parameters controlling the transparency of pixels used to display banner ads.
