Quote

Antivirus firm Avast has admitted inadvertently distributing a trojanised version of CCleaner, a popular PC tune-up tool, for nearly a month, infecting an estimated 2.27 million users….Cisco Talos discovered that servers distributing the program were leveraged to deliver malware to unsuspecting victims.

“For a period of time, the legitimate signed version of CCleaner 5.33 being distributed by Avast also contained a multi-stage malware payload that rode on top of the installation of CCleaner,” researchers explained. “On September 13, 2017, Cisco Talos immediately notified Avast of our findings so that they could initiate appropriate response activities.”

CCleaner has been downloaded over 2 billion times, with 5 million additional downloads a week.

We estimate that 2.27 million users had the v5.33.6162 software, and 5,010 users had the v1.07.3191 of CCleaner Cloud installed on 32-bit Windows machines. We believe that these users are safe now as our investigation indicates we were able to disarm the threat before it was able to do any harm.

There is no indication or evidence that any additional malware has been delivered through the backdoor. In the case of CCleaner Cloud, the software was automatically updated. For users of the desktop version of CCleaner, we encourage them to download and install the latest version of the software.