I have not updated CCleaner since v5.46, some 14 version changes ago, which Piriform popups keeps reminding me. The inference in the popup is that I am not fully cleaning. Ridiculous! CCleaner is not a security product. I have not seen any fixes since v5.46 that have addressed any security concerns. My old version continues to work well. Piriform lost my trust when they tried to sneak an AV onto my PCs, and now they want to sneak in this CC browser. I am also being constantly nagged with offers to upgrade to the paid version of CC. I intend to stick with this old version, intil it irritates me enough to ditch it.

If I had my way, I'd still be using CC 5.0.8... which (if memory serves me) continues to run on my Win8.1 tablet using Windows Defender.

Unfortunately, avast insists on automatically updating CC... I believe to at least version 5.41, which is what I (I think I) have on my WinXP laptop.

For better or worse, I've advanced to CC 5.56 on my Win7 laptop... the 5.41+ forced by avast, and the subsequent update in contemplation of migrating to Win10 (which "failed").  

My understanding is that Win10 likewise requires "relatively new" versions of CC for "compatibility".