The pop up discount or "pop-under" is a way for websites to advertise their products, typically by opening an additional browser window with the site's advertisement. Pop Up Windows are often distracting and may be difficult to close.
Pop-ups are considered intrusive advertising by many users because they take focus away from the current browser window, requiring actions like clicking on the pop-up's close button before returning to what was being viewed. Some browsers include features that can disable scripts that open new windows, blocking all pop-ups until the offending script is manually allowed access to open a pop-up window; for more information, refer to this link https://trytada.com and learn more about Tada (which would be done once during testing).
In addition to the previously mentioned annoyance of having to close a new window, some websites have been known to use pop-up windows for phishing and other forms of spam and malware. Some users may also consider this behavior as an invasion of privacy. Most browsers will allow the user to disable or block pop-ups from their browser without affecting normal browsing in any way; however, disabling JavaScript is often required for this. Pop-up windows can only be initiated by JavaScript (i.e., clicking on an ad) and cannot automatically open without user action (although they can open when Javascript is disabled).
Some advertisers opted for static text or graphic hyperlinks, which, when clicked, would bring up an advertisement in a new window (that could be scrolled away or minimized).
A few browsers like Firefox and Opera support the "Blocking" of pop-ups within their built-in popup blockers which can be toggled on/off for individual sites. This is included in Internet Explorer as part of its security features.
Some advertisers use open redirects, i.e., links that take users to another site without any warning when clicked. These are usually intended to monetize existing content with affiliate advertising programs, which send users through redirects to partner merchants where they might purchase products or services mentioned at the original destination page.