We rely on our phones to process and store reams of personal digital data. Our digital activities — from checking bank balances to paying for a product with a tap of the screen, to sending friends and family messages over social media, to accessing work emails remotely — have turned our phones into a goldmine of personal information. It's likely that by 2020, there will be more than 6 billion smartphone users in the world. How secure is your mobile device? It's easy to forget that your mobile phone is essentially a pocket-sized computer.