Have you seen a pop-up alert saying your computer has been blocked and you need to call an 800 number to unlock it? What can you do to avoid this kind of scam? First, to get rid of the immediate problem, either close the pop-up window or if that doesn’t work, force-quit the browser: Hit the Command, Option and Esc keys on a Mac or the Ctrl, Shift and Esc keys in Windows, select the browser, and click “Force Quit” on a Mac or “End task” in Windows. Then read “Don't let sketchy pop-up ads scare you” on the USA Today site to understand more about where these scams come from and how to minimize your risk .