Malware alert!

I have just had a screen appear on my iMac which claims my machine is infected by multiple virus's! Looking at the URL it does not look genuine but I am worried! The URL is d35oxjtzhfo1g2.cloudfront.net and shows the secure symbol padlock. The message reads "Your System is infected with 3 viruses" and "Personal and banking information is at risk" and tells me to click on a button labelled Scan Now. There is also a red Apple logo claiming to be AppleCare Protection Plan.

Am I at risk and what should I do to remove this from my machine? I have a screenshot, see below