[jQuery] Detect browser close event

[jQuery] Detect browser close event

How can i detect browser close event?
I've tried something like:
$(window).unload(
   function(){
      alert("close");
      //stop event
      return false;
   }
);
Alert appears, but event continues...
Thx!<br clear="all">
--
Unai Martinez
<a href="mailto:unai.martinez@gmail.com">unai.martinez@gmail.com</a>
<a href="http://helusinfa.blogspot.com">http://helusinfa.blogspot.com</a>
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