Security firm ESET found that the campaign, called Stegano, was widely disseminated as banner ads on major websites. The malware creators manipulated an image so that it contained a data structure. The data structure could then be decoded by the victim machine and carry out the malware authors diabolical plans. The big advantage is that the image will look unchanged to normal observers unless they conduct a detailed examination. That means the fraudsters can distribute the image more widely, since it appears harmless.”]
Source: https://securityintelligence.com/news/malvertising-poisons-banner-ads/