These types of ads became
popular in the second half of
calendar 2001. Reasons most
advertising agencies gave for this was due to
backlash to pop-up ads, and feature media coverage about reader anger towards them.
Facing client questions about why the client's media agency encouraged them to use a technology that associated the client with negative press, agencies began recommending pop-under ads. The companies that switched to these were primarily companies worried about brand management, whereas companies like X10 continued to use pop-up and pop-under ads.
Media agencies have begun to pursue other types of even more intrusive ads, like shoshkeles. These are ads that appear *over* the page itself, and carry out some sort of animation. United Virtualities is the company responsible for these.