I just installed CCleaner. When I clicked the download, Google Chrome gave me a warning that "This type of software can harm your computer." I'm new to Chrome so maybe it says that about all .exe files. My wife had CCleaner installed by Best Buy, so I continued.
During installation, my Symantec system protector gave me the following notice:
Or if you downloaded from one of the official download sites listed above what your av may be detecting is the Yahoo Toolbar, since some antivirus may deem toolbars as a risk and flag them however you can always opt out.