First, there is no such thing as a "/who hack"...
Because all this stuff is server side because Blizz takes your IP down when you log on the server, when you log out, the 20 second wait is partly for the IP removal from the server data, and second... If this was possible your friends could see you online anyway, this means you should have two hacks.. Thirdly, we see the guy kill a mob with 1% hp, and it we have no proofe of if its not an emulated server, and this thing sounds too good to be true anyway, Might be a nice scam to get a Really good hack... Tough I know there is a hack called Stealth.exe that makes you "stealthed" in the /who list, but friends could still see you, But it needs a log in to your account or some site which you get it, I tried it, entered some shit on the Account: and the Password: , and I "logged in" Tough thanks to my firewall it blocks everything in and out of my computer, I think its a scam for peoples accounts.. Thats my tought...