Efficient Javascript Pop-Under Script

Avg Bid (USD)
Project Budget (USD)
$150 - $250

Project Description:
To job is very simple to be explained, but not very easy.
I need a javascript code that will show a pop-under window.
This pop-under code will be embed in a website, the hard part is that the pop-under must reach min 90% of the website visitors.
P.S. I want pure javascript, no jQuery.

Skills required:
AJAX, Javascript
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