Random Pop up - Malicious "Captcha"?

Hello, 

I was just adding some coins a couple of minutes ago, and added my first Chilean coin ever. I wanted to see it on the map, hence went and took a look. While I was doing so, the Numista page (not the screen itself) went black and a captcha test popped up. I thought that was strange and didn't perform the captcha, instead I took a look at the web address bar. It displayed not Numista but some random “ddq……” site name, and thus I simply clicked the back button and went to a different page on Numista itself. I don't have a screenshot (should've taken one in hindsight) but thought I would put this out there. First time something like this has happened. 

Rajbarage

Hello,

This is most probably caused by some external browser plugin or other app installed on your device.

Xavier

Hello,

This is most probably caused by some external browser plugin or other app installed on your device.

I am not so sure now. I got something similar again, and I spend a lot more time on other sites where I don't get such things. I was attempting to add a coin when it popped up, specifically on the tab where I was adding the coin. Just this morning, I reviewed all of my downloads in the past month, and checked for bugs. 
Here is the screenshot. 

Rajbarage

Xavier

Hello,

This is most probably caused by some external browser plugin or other app installed on your device.

I am not so sure now. I got something similar again, and I spend a lot more time on other sites where I don't get such things. I was attempting to add a coin when it popped up, specifically on the tab where I was adding the coin. Just this morning, I reviewed all of my downloads in the past month, and checked for bugs. 
Here is the screenshot. 

Just happened again, right as I was about to send the page for review. 

Edit: Looked it up, apparently it is an advertiser issue normally.