A newly discovered variant of the notorious Zeus banking trojan is disguising a crucial configuration code in a digital photo, a technique known as steganography.
Zeus is one of the most effective tools to steal online banking details, hijacking login details as a person accesses his account and masking secret transfers in the background.
The variant, called ZeusVM, downloads a configuration file that contains the domains of banks that the malware is instructed to intervene in during a transaction, wrote Jerome Segura, a senior security researcher with Malwarebytes. He wrote the behavior was first noticed by a French security researcher who writes under the name Xylitol.
"The malware was retrieving a JPG image hosted on the same server as were other malware components," Segura wrote.
Steganography has long been used by writers of malicious software. By embedding code in a file format that looks legitimate, there's a chance the file will be given a green light by security software.
"From a webmaster point of view, images (especially ones that can be viewed) would appear harmless," Segura wrote.
The suspect image appears to be much larger when compared to an identical one in bitmap mode, he wrote. The data added by the cybercriminals had been encrypted using Base64 encoding and then RC4 and XOR encryption algorithms.
When decrypted, the file shows the banks targeted, including Deutsche Bank, Wells Fargo and Barclays.