We would like to apologize for a security incident that we have recently found in CCleaner version 5.33.6162 and CCleaner Cloud version 1.07.3191.

Source
Update

Cisco Talos wrote about it
This is also an interesting post by Malwarebytes

Was Iinfected?

Thankfully, it looks like this malware only affected a certain subset of CCleaner users. In particular, it affected:

• Users running the 32-bit version of the application (not the 64-bit version)
  *Users running version 5.33.6162 of CCleaner or CCleaner Cloud 1.07.3191, released on August 15th, 2017

If that version is before version 5.33.6162, then you are not affected, and you should manually download the latest version now. If that version is 5.34 or later, your current version isn’t affected, but if you updated CCleaner in between August 15th and September 12th, and are on a 32-bit system, you may still have been affected. (If you’re comfortable going into the registry, you can open Registry Editor and navigate to HKLM\SOFTWARE\Piriform and see if there is a key labeled Agomo:MUID . If that key exists, it means you had the infected software on your system at one point in time.)

What Should I Do?

While nothing immediately harmful was discovered, Cisco Talos recommends restoring your system to a state before August 15, 2017 from a backup if you were affected. You should probably run an antivirus and MalwareBytes scan on your system and your backups to ensure no malware is left installed.

Source: howtogeek.com