Hiya folks. I didn't see a topic on this, so I thought I would start one. Many of you may already know. I'm also a little late to the party (news was broken on Monday by Cisco Talos).
If you downloaded version 5.33 of CCleaner recently, you also downloaded a multi-stage payload on top of it. It looks like it was a watering hole attack, so it's unlikely the payload will DO anything to you (they were supposedly targeting big tech giants, including Cisco themselves), but you still don't want a mysterious malware backdoor on your PC. Cisco recommends you not only uninstall CCleaner, but also re-image your machine (or just restore to a date prior to August 15th). If you really want to keep CCleaner, then update to 5.35 immediately.
Thank god I didn't install that update (still on 5.23).
More info:
http://blog.talosintelligence.com/2017/09/avast-distributes-malware.html
http://blog.talosintelligence.com/2017/09/ccleaner-c2-concern.html
http://www.techrepublic.com/article/ccleaner-hackers-attacked-microsoft-intel-cisco-and-other-tech-giants/
https://www.pcworld.com/article/3225407/security/ccleaner-downloads-infected-malware.html