How did they do that?!?

Tonight, I went to http://www.adcritic.com/

As I started to browse, all of a sudden the contents on the screen began to
fade out, and a large graphic animation of a phone appeared enticing me to
click on it.  I avoided the temptation, and after choosing "close window"
this "layer" disappeared, and the contents behind it slowly faded back in
and I was able navigate the site.  While horrendously annoying, this is one
of those time where I was left scratching my head.  They cookie the site so
if you want to do it more than once you'll need to clear your cookies out.

It appears the ad is in Flash.  But how it's interacting with the rest of
the page, and the fact that it doesn't even hint to what it's doing in the
source, leaves me scratching my head.

How did they do that?

HWG hwg-techniques mailing list archives, maintained by Webmasters @ IWA