Re: How to stop Viber running
How to stop Viber running without uninstalling it?
You can try any of these three methods (presuming you're referring to the Windows Phone 8.1 version of Viber):
1. Go to Settings > Battery Saver > prevent Viber from running in the background;
2. Launch your Viber app, go to the settings > notifications > disable everything you find in there;
3. Launch your Viber app, go to the settings > privacy > deactivate account. Of course, you would have to re-register your device into Viber after this method.
Hope these help.