I am sure that there is a misunderstanding somewhere. I never ever saw any pop-up advertisement on PPRuNe.
A pop-up is actually an advertisement or announcement in a new browser window, mostly in a resized and much smaller window, frequently also programmed to stay open as long as the "main" window is visited.
What we have here on PPRuNe are simply advertisement banners, created as still pictures, animated gifs or even as a little Flash movie.
These banners may be as nasty as a new browser window as they can be programmed to contain spyware etc.
As already mentioned here on the thread earlier, there are means to avoid the banners coming up...AdAware and the one mentioned here as well as plenty of others may help. Using these "protective" measurements will on the other hand create error messages in IE as a script error is suspected due to the fact that a component of the webpage is not loaded.
So...if you see a pop-up (and this means a new browser window), it does not come from PPRuNe...