Often containing advertisements, pop-ups are windows users encounter when they enter a web page. Pop-ups may not necessarily contain ads; in some cases, they may also feature forms embedded by webmasters who want to collect information. Pop-ups are considered to negatively affect user experience, therefore not recommended by webmasters unless it's a necessity. Especially pop-ups where the closing button is hidden or very hard to find will most likely cause users to leave the web page.
