Legitimate Virus Warning from Apple?

I just finished starting from scratch, wiping my iMac hard disk and installing a new version of High Sierra. I also installed Logic Pro X and EZ Drummer.

I purposefully did not install any email programs because I did not want to risk getting a virus on this iMac, which I am reserving only for use with Logic.

I went to download my seriel number for EZ drummer from the Toontracks site, and suddenly the window and message that is posted below in the screenshot came up. Is this a legitimate message from Apple? I did not select Scan, because I was not sure if this was legit or a trick.

I thought I'd ask here first.

What should I do?

Thank-you for your time and expertise!