From the Nokia Store description:
A simple widget to start and stop completely WhatsApp.
Content can only be accessed through Home screen > Widget catalogue. No icon in Menu & pressing launch in store client will not do anything! You need to go to homescreen and select add widget.
You need WhatsApp to be installed on your phone.
Here's the somewhat minimal 'interface'(!):
Nokia Innovation comments:
The thing I love about it, is that it doesn’t open up another UI screen, it just turns green or red. Why would you want to switch WhatsApp off anyway? Well it can be a bit of a battery drain especially if you’re not using it and don’t need it running in the background. Having complete control over it is exactly what us Symbian users like!
Interestingly, the widget is based on unsigned code from @Huelif and other code snippets are planned to be published soon, including a similar widget to kill all background map services (e.g. to free up RAM or compass functions).