Two unknown pop ups have seized my screen and I can't make them close

A pop-up is prompting me to download an unknown downloader. I don't want it and cannot make it go away. Next, an error message pop-up sprang up a few minutes later warning of a security breech and to get me to call an 844 ph. A web page from "Realitieswatch.com" is now on the screen.

I'm running OS X on a Macbook Pro Retina.

Who are these folks? Is this malicious? Thanks for any help.