Not that we condone this type of prank but there are a few things you can do. Firstly using transparency to hide the window is ok but you can use ShowWindow instead.
Firstly the function Huhu_ChatWndReceiveMessage doesn't appear to be called anywhere (unless there is parts of your script missing).
Secondly this line
Javascript code:
var tmp = (Message, "[alpha]");
will not do what you are expecting it to do. I presume you are wanting to split the string or replace the script or something...
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