Now, something worth noting.... all of this "stuff" is NOT the so called "fault" of this site.
We enjoy a great site. They sort of HAVE to support this through adds. So our site does it's BEST to deal with legitimate Add groups, as third party's. No different than hundreds of other sites. Look, these folks need SOME income?
Generally, Malware and Virus agents will come at you via add sights. Think like a crook - this is the very BEST way to wack a load of computers.
What to do?
1) If you can, screen capture the pop-up as a jpg.
2) KILL your web browser, via task manager - click on NOTHING.
3) If you HAVE a firewall (and you should) - use NSLOOKUP and WHOIS to find the domain of the pop up, or Malware. BLOCK all communication, in or out, with that entire domain.
Example: I got a wack, via an embedded add, from d38ybipedeka5t.cloudfront.net (my original post). NSLOOKUP told me the four addresses that this Malware Site used. I used my great Synology Firewall to BLOCK all traffic from this entire subnet. Boom - no more issues.
Now - if all too technical? Remember 1), and 2). DO NOT CLICK ON ANYTHING - KILL BROWSER. In my case? AVAST FREE did a great job minimizing any potential damage.
PS - Browser? Latest Chrome. Chrome, by itself, won't save you. Have a good Virus Checker - AND a Firewall.
Data on who, exactly, cloudfront.net IS ....
https://www.quora.com/What-is-CloudFront-net-adware