wp-admin login page says update database

When I go to my wp-admin login it opens a page saying Database Update Required
“WordPress has been updated! Before we send you on your way, we have to update your database to the newest version. The update process may take a little while so please be patient.”
And button: “Update WordPress Database”

I have never seen such a thing before. My website is currently under attack (IPs getting locked out for too many failed login attempts several times a minute) so I suspect some sort of hoax. Is it a hoax? How can I log onto my website??