If it is a pop-up notification in Safari browser it is not really a virus, in that case it is just an undesired notification from a real or faked McAfee we site. You can go to Safari Preferences/ Settings/ Websites / Notifications and remove all sites listed (or at least those that you do not actually want).
This. And whatever you do, don't download McAfee. There are a lot of sites purporting to have loads of user manuals on them, I just did a little test Googling "Worcester Bosch Heating Manual' as a search string and one of the top hits was an extremely dodgy looking site 'FreeBoilerManuals.com'. The name itself was enough to get me alarmed, let alone the appalling front page design. I wasn't prepared to even click on the apparent cookies acceptance dialog.
For stuff like this, always go to the manufacturer's site.
