Microsoft Defender Antivirus flags certain CCleaner installers as potentially unwanted software according to a new database entry on the company's malware encyclopedia site.
CCleaner is a popular tool for Windows to remove temporary files to free up disk space. It comes with several other features including options to update installed programs, run a health check, or clean the Registry.
Potentially unwanted software is not outright malicious, but as the name suggests, may be unwanted by the user. A common form of these kind of applications bundles other, often third-party software, with the installer; this is done by the company for financial reasons or to push some of its other products. Often, these offers are checked for installation by default, or the installer is designed in a way that may confuse the user in installing the offered products.
Some of CCleaner's installers bundle third-party software. Microsoft lists four products on its site of which two are owned by Avast: Avast Free Antivirus and AVG Antivirus Free. The installer may also offer Google Chrome or Google Toolbar but there are probably more offers such as CCleaner Browser (it used to be offered some time ago at the very least).
Here is Microsoft's description:
Certain installers for free and 14-day trial versions of CCleaner come with bundled applications, including applications that are not required by CCleaner or produced by the same publisher Piriform. While the bundled applications themselves are legitimate, bundling of software, especially products from other providers, can result in unexpected software activity that can negatively impact user experiences. To protect Windows users, Microsoft Defender Antivirus detects CCleaner installers that exhibit this behavior as potentially unwanted applications (PUA).
Microsoft Defender Antivirus flags these installers provided that you have enabled the protection against potentially unwanted software. The company notes that the programs that come bundled with CCleaner are not malicious in nature, but that they may be unwanted by the user who runs the installer.
This is the second time that Microsoft blocked CCleaner; the first incident was on the company's Answers forum on which CCleaner's domain was banned for some time. Microsoft stated later that the banning was erroneous and removed the blocking again.
Windows users who want to use a software to clean temporary files may want to check out Bleachbit, an open source program that provides similar functionality.
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