This seems to be new  and spreading

rogue  chrome scareware_riser

I noticed this pop up today  when i opened up a website in chrome browser

adshownow.com/jquery-1.5.2.min

 

My avg virus scanner   decided this a  harmful code and flagged it as  

"Exploit Rogue Scanner (type 1292)"

 

Any help would be  Nice !! anyone

I ve seen a  similar report here