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Any time I'm on a site that does this, I immediately close the page. I don't care how interesting the article is. Even if it's lifesaving advice that I need to read or I will die RIGHT NOW, I close the page as soon as that pops up. It's intrusive (or obtrusive?), and it's terrible site design.
If your website does this, you need to unplug your web server from the internets immediately.