Pop-up Ad

A Pop-up Ad is an advertisement that is displayed suddenly while a user is surfing or visiting a specific Web site.

On legitimate Web sites, Pop-up Ads are merely a nuisance. However, when the user clicks on a malicious Pop-up Ad, a drive-by download can be triggered. That is, a Pop-up Ad could launch a process that downloads Spyware. Pop-ups can be vehicles for one of the most virulent Spyware distribution schemes: the ActiveX drive-by download.

A persistent stream of Pop-up Ads can use up enough of a computer's disk space, bandwidth and memory to cause the machine to slow down or even crash. Malicious Pop-up Ads can also compromise browser performance and install unwanted desktop icons.

Although Pop-up Ads are not, strictly speaking, Spyware, they are most effective when guided by Spyware.