I too rece3ived this malicious popup

I see where you also have received this popup that runs a scan on your computer and tells you that you are infected and to buy there product to fix it. I don't understand how this popup is getting through. I have microsoft security as well as norton internet security yet I still received this popup. If I hadn't seen it before I wouldn't have known what it was. I simply did a ctrl alt delete and shut down the internet. How did this get through when I supposely have all this internet security installed?