So, you've had it with popups and popunders, those annoying advertisements on the web that open a new web browser windows without your permission and chew up the valuable Internet bandwidth that you're paying for!
I bet you've even tried to install or turn on "popup blockers" and found that that they're not 100% reliable. That's because that class of software has to try and guess the difference between a window you asked for, and a window that probably contains an ad, and that's impossible to do with 100% accuracy.
Think that sounds dangerous, like some kind of computer virus? You're not far off the mark. The web browser companies put this technology into the web browsers over the objections of the entire computer security community, because they were listening more to the web site designers. The designers wanted more control over how the web browsers displayed web pages, and to try and prevent the users (that's you) from doing things they didn't like.
My computer is my own to control and use. It offends me that any web site designer thinks s/he should be able to take it over even a little bit.