There's two different things going on.
- There was in fact an error with WhatsApp accessing something it wasn't supposed to causing a Prevention popup.
- This is a Security Policy Update direct from Samsung that is being pushed out. Unfortunately the servers are backed up as noted earlier. http://www.geeky-gadgets.com/samsung-galaxy-s4-update-released-23-09-2013/
Maybe WhatsApp doing whatever it did forced your phones to trigger an update request earlier than others as everyone else seems to have started getting it yesterday. So far I've only seen posts from people in the EU region though.
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If it ain't broke, use a sledge hammer.