How to Close a Suspicious Warning in Safari on a Mac

What you need: A Mac with a suspicious warning open in Safari.

Before you begin: Do not click inside the warning, call any phone number it shows, or type anything. Ignore any button in the warning that says it will close the warning.

Steps

1. Look at the top of the screen. If the warning fills the whole screen and you cannot see Safari's toolbar, the strip with the address box where a website's address is shown, press the Esc key, in the upper-left corner of the keyboard. The warning moves back inside the Safari window, and the toolbar appears. If you can already see the toolbar, go on to the next step.
2. Look near the top of the Safari window. If you see a row of tabs, the highlighted tab belongs to the page showing now: the warning. If there is no row of tabs, the warning is the only page in this window.
3. If you see a row of tabs, move the pointer over the warning's tab. An X appears at the left end of the tab. Click the X. If there is no row of tabs, click the red button in the upper-left corner of the Safari window instead. The warning closes, or a box asks whether you are sure you want to leave the page.
4. If a box asks Are you sure you want to leave this page?, click Leave Page. The warning closes.
5. If the warning is still showing, quit Safari. This closes all its windows, and anything you typed on a page but did not send may be lost. Click Safari in the menu bar at the top of the screen, next to the Apple logo, then click Quit Safari. If Safari asks whether you are sure you want to quit, click Quit. If a box asks Are you sure you want to leave this page?, click Leave Page.
6. If you quit Safari in step 5, the next time you open Safari, hold down the Shift key, and while holding it, click Safari (a blue compass) in the Dock, the row of app icons along the edge of the screen. Keep holding Shift until a Safari window opens, then release it. Holding Shift stops Safari from reopening the windows it had open, including the warning. If the warning appears again, go back to step 1.
7. If you installed something from the warning, shared personal information, or allowed someone to control the Mac, stop following their instructions and contact Apple Support. If you gave payment details or sent money, also call your bank using the number on your card.

Expected result: The warning is gone. Safari shows your other pages, or its window has closed and no warning is on the screen.