Don't fall for this. It's a SCAM, not a scan. Ha! See what I did there? I crack me up!
But, seriously, I have perfectly good antivirus software (Kaspersky) on my PC which already routinely catches and prevents virus/dangerous downloads. That's how I know that while browsing a legitimate TV news channel's site and clicking one of their ads (which I do as a token of appreciation for their content), this pop-up that appeared is in fact bogus.
See screenshot, below. Don't fall for it!