Pop-up on my iPhone in Safari

Right now, I am forced to be in the tab section of the Safari app on my iPhone because there is a horrible virus pop-up that says "http://system-alert-test-result.in Online browser security has detected virus attack...... call toll free number." But every time I press okay, it just pops right back up before I can do anything. So I have been unable to use my Safari app on my phone. HELP!