Netscape 4.x Full Screen Ads

We use Netscape as our main browser – and email client – Starting last week, when you open Netscape Messenger – the ad/news that normally opens in the lower preview window now opens in a seperate full screen page. This is most likely NOT a setting on the PC as it started happening all at once – and on several hundred machines the same day. If the preview window is closed the ad/news page does not load – however if it is open, it opens in a seperate window – Not a very big problem, but those of you in Desktop Support will understand that ANY extra click a user has to do that takes them away from their Solitare playing duties makes them call for support. Has anyone else seen this issue with Netscape (4.x, maybe 6.x too)?