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A variation on the pop-up window, the pop-under advertisement, opens a new browser window under the active window. Pop-unders do not interrupt the user immediately, but appear when the user closes the covering window, making it more difficult to determine which website created them.
Pop-up ads originated on the Tripod.com webpage hosting site in the late 1990s. Ethan Zuckerman claims he wrote the code to launch advertisements in separate windows as a response to complaints of displaced banner ads. He didn't invent the pop-up window. Zuckerman later apologized for the unforeseen nuisance pop-up ads had evolved into.
Web development and design technologies allow an author to associate any item on a pop-up with any action, including with a cancel or innocent looking button. Because of bad experiences and apprehensive of possible damage that they may cause, some users do not click on or interact with any item inside a pop-up window whatsoever, and may leave the site that generated them or block all pop-ups.
Opera was the first major browser to incorporate tools to block pop-up ads; the Mozilla browser later improved on this by blocking only pop-ups generated as the page loads. In the early 2000s, all major web browsers except Internet Explorer let users block unwanted pop-ups almost completely. In 2004, Microsoft released Windows XP SP2, which added pop-up blocking to Internet Explorer. Most modern browsers provide pop-up blocking tools; third-party tools add other features, such as ad filtering.
Users of websites and web applications continuously experience unwanted pop up ads through the course of their normal interaction with a web browser. Ordinarily, users respond by dismissing the pop-up through the "close" or "cancel" feature of the window hosting the pop-up. Because this is a typical response, some authors of pop-up advertising depend on this, and create on-screen buttons or controls that look similar to a "close" or "cancel" option. When the user chooses one of these "simulated cancel" options, however, the button performs an unexpected or unauthorized action (such as opening a new pop-up, or downloading an unwanted file on the user's system).
URLs are sometimes redirected to advertisement pages by URL redirection.
URLs are sometimes opened in a new tab and then the content of the old background tab will be replaced with an advertisement page by URL redirection. Adblock Plus,uBlock, or NoScript, cannot block these pop-redirects.
Pop-under ads are similar to pop-up ads, but the ad window appears hidden behind the main browser window rather than superimposed in front of it. As pop-up ads became more widespread and more intrusive, often taking up whole computer screen, many users would immediately close the pop-up ads that appeared over a site without looking at them. Pop-under ads do not immediately impede the view of content, but remain unnoticed until the user closes or minimizes the main browser window.
// create a new window in front of the current site window.open( URL, windowName[, windowFeatures] ); // push the loaded advertisement back behind the browser window.focus;
Most modern browsers allow
window.open to execute only if it was called by a user interaction (e.g., a mouse click) event handler. Any non-interactive calls (timer callback, load events, etc.) to
window.open result in the new window being blocked.
To bypass this restriction, most pop-under ads trigger on a mouse click event listener attached directly to the document or the document's body. This enables catching all mouse click events that were not consumed by other click event handlers, and calling
window.open without being blocked. For example, when the user selects a text, the mouse click triggers the mouse click handler attached to the document and a pop-under opens using the above code. Notice that there are more techniques to bypass the
window.open call restriction by "hijacking" mouse clicks.
Copyright aspects of pop-up advertising are discussed in the like2do.com resource articles Derivative works and Transformativeness. Both articles contain illustrations and links to examples of pop-up advertising.