When you close one app and move to another, the previous app is still running in the background – this is known as a ‘Session’.
To truly close the session, shut down the app and ensure the PIN lock is activated, follow these steps:
Double-tap the home button to reveal the apps running in the background – they will be displayed in a cascaded/tile view as shown below:
Place your finger on top of the VBR app tile and, without your finger leaving the glass, slide the tile up and off the top of the screen.
Once the app has disappeared off the top of the screen, the app is fully closed.
Note: this enforces PIN lock but is also a good trick for preserving and prolonging your battery life – the more apps running in the background the more power the device is using.