http://warning3.media4.netdna-cdn.com

I just returned from a coffee break and logged back onto my mac and opened Safari. Suddenly I got this supposedly official looking Safari warning. It says serious vulnerbilities on my MAC might have been found on this date and this time. Call1-888-996-0235 (Toll Free) for immediate assistance.

I know this is something malicious so I did not click anything and force quit Safari. Then opened Safari again and the message comes back. I logged out and shut down the Mac and then restarted. Opened Safari and this same message comes up. HELP! How do I get rid of this without compromising my Mac?