I currently have version v6.17.10746 (64-bit) installed
In the program main window, when I click on the link ‘Check for updates’
at the lower right corner a pop-up window shows up saying there is a new version available. When I proceed to update the download starts but when reaching 100% it gets stuck and never proceed.
Your title is “Anti-Virus Warning”; but you post does not mention any AV at all.
Why do you think that an Anti-Virus is involved here?
Are you getting a warning? If so then what is it and what AV is it from?
Being practical:
Download a Standard installer from here: Download CCleaner builds | CCleaner Portable, Slim, and more
Double-click the downloaded file to install the latest CCleaner version.
There is no need to uninstall your old one, the new one will simply overwrite it.