The second stage appears to use a completely different control network. The complex code is heavily obfuscated and uses anti-debugging and anti-emulation tricks to conceal its inner workings. Craig Williams, a senior technology leader and global outreach manager at Talos, said the code contains a "fileless" third stage that's injected into computer memory without ever being written to disk, a feature that further makes analysis difficult. Researchers are in the process of reverse engineering the payload to understand precisely what it does on infected networks.
"When you look at this software package, it's very well developed," Williams told Ars. "This is someone who spent a lot of money with a lot of developers perfecting it. It's clear that whoever made this has used it before and is likely going to use it again."
Stage one of the malware collected a wide assortment of information from infected computers, including a list of all installed programs, all running processes, the operating-system version, hardware information, whether the user had administrative rights, and the hostname and domain name associated with the system. Combined, the information would allow attackers not only to further infect computers belonging to a small set of targeted organizations, but it would also ensure the later-stage payload is stable and undetectable.
Now that it's known the CCleaner backdoor actively installed a payload that went undetected for more than a month, Williams renewed his advice that people who installed the 32-bit version of CCleaner 5.33.6162 or CCleaner Cloud 1.07.3191 reformat their hard drives. He said simply removing the stage-one infection is insufficient given the proof now available that the second stage can survive and remain stealthy.