Hello, my name is Rusty. Your phone has been hijacked. It's not a bad scenario, they just want you to pay money to remove the message. It's a scam, not a real warning.
Choose Force Quit from the Apple menu, close Safari, and then launch it with the Shift key held down. If that doesn't work, temporarily disconnect the computer from the Internet and/or click here and run Adware Medic. You may need to download it from a different web browser.