This might seem like it should be going to a webdev list, but there's a possible security implication, so here goes;
http://2-spyware.com/file-cnfrm-exe.html
In Mozilla 1.5 and FireFox 0.9 with the pop-up blocker turned on, I get a pop-up! It's purporting to be an important notice from my Network Administrator - you'll probably recognise it;
http://2-spyware.com/images/2SPYRR1C.gif
Surprise! It's not actually a popup - just an image floated above the web page. Annoying, yes, but not an actual window, and therefore not really a popup (at least, not one of the sort that Mozilla tries to block).
PGP.sig
Description: This is a digitally signed message part
