I don't know how this got past me for so long, but I only have learned of it about 2 months ago. But "Is CCleaner still safe" has been a question being asked a lot over the past couple of years. At one time, CCleaner was great, did a good job and was easy to use, but something had changed, and we will get into that in a bit. Overall, what my research has turned up has gotten me to stop promoting the software, and now recommends people to uninstall it now.

Lets first talk a little about Avast, before we get into CCleaner. We all should know now that data collection is a given on the web and there is a level of trust that is given for those websites, software, ect..., to give a level of knowledge so you know and can opt out if you like. Well Avast is a Free Anti Virus software that is pretty well known. Earlier this year, they were exposed for tracking users clicks and movements across the web, collecting data on things like Google searches and visits to LinkedIn pages, YouTube videos, and pornography websites. With that data they were collecting, they say they "De-identified" the users, then has been sharing personal info collected from their devices with a subsidiary that sells trend analytics to Google, Home Depot, Microsoft, and Pepsi, without any way to opt out.

This had put may people a little bit uneasy. Because of the backlash from their users, they have taken steps to allow you to disable the telemetry.

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Would I suggest people not to use Avast, not quite yet. What I can see, they are still good especially being free, and having the ability to now control what they gather is a plus.
Windows does the same thing, - Read about it here:

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Now you know what we are dealing with here, lets get back to the question, is CCleaner safe.
Before I would have said yes, however, now the reply is not so sure. Several major issues showed up since CCleaner has been hacked at the end of 2017. The hack put 2.27 million PC users at the risk of being infected by malware. After that, the question “is CCleaner safe 2018” is frequently asked by Windows users. The most curious thing is that this happened after Avast acquired the application developer company in July of 2017.

Fortunately, this issue was solved when it was found and updated automatically. Is CCleaner safe now? Probably not. There are other issues that also put PC users at risk.

• Update without users permission: CCleaner silently forces updates to users and ignores users’ preferences about checking for updating. There are PC users complaining the issue on the forum that CCleaner has already updated to his system automatically without his permission.
  
• Enable Collection Options: CCleaner even enables collection options (to collect users system information) by default in the latest version.
  
• Monitor users system information: The loudest sound comes from the CCleaner version 5.5. A feature called “Active Monitoring” is used to collect anonymized information related to users systems. You can disable it or turn it off, but the software will reopen it again when rebooting or reopening CCleaner.
  
• Hard to exit: Though you click the close icon to turn it off, it will minimize to your System Tray. When you right-click its icon, there was even no option to exit. You have to exit CCleaner via Task Manager. If you are a novice user, you won’t know how to close it.
  
• CCleaner had malware: The 32-bit version was infected with Trojan, which collected the version’s installation system information. In addition, the Trojan had the capability to run codes on the influenced systems. Though CCleaner company captured it before it is spread in a more large-scale, Avast company still suffered from the malware of CCleaner.

Overall, the trust of CCleaner has gone down and it seems most tech sites have been suggesting uninstalling it and using something else.
That's where my Utility script does come in. It uses no outside software to do what those apps do, everything it does is using the tools that Windows already comes installed with.

So, Overall. Now you know why many are saying not to use CCleaner, and if you have it now, uninstall it. It's also why you won't be seeing me recommending it anymore.