Since October, millions of internet users have been exposed to malicious code served from the pixels in tainted banner ads meant to install Trojans and spyware, according to security firm ESET.
The attack campaign, called Stegano, has been spreading from malicious ads in a “number of reputable news websites,” ESET said in a Tuesday blog post. It’s been preying on Internet Explorer users by scanning for vulnerabilities in Adobe Flash and then exploiting them.
The attack is designed to infect victims with malware that can steal email password credentials through its keylogging and screenshot grabbing features, among others.
The attack is also hard to detect. To infect their victims, the hackers were essentially poisoning the pixels used in the tainted banner ads, ESET said in a separate post.
The hackers concealed their malicious coding in the parameters controlling the pixels’ transparency on the banner ad. This allowed their attack to go unnoticed by the legitimate advertising networks.