CCleaner maintenance software, owned by Avast, should be updated immediately as criminal hackers appeared to have installed a backdoor into almost 2.27 million downloads.
Run the updater, and by all means, run an a/v and security scan.

Further investigation found the CCleaner download server was hosting the backdoored app as far back as September 11. CCleaner For Windows Found to Have Backdoor [forbes.com]

"The threat has now been resolved in the sense that the rogue server is down, other potential servers are out of the control of the attacker.

"Users of CCleaner Cloud version 1.07.3191 have received an automatic update.