The free calling and messaging app Viber could be letting hackers gain control of your Android phone by bypassing the lock screen.

Discovered by a Vietnamese security firm, the possible security breach allows attackers to scoot round the phone's lock screen before gaining access to the phone's controls and everything else stored within.

Much like Skype, Viber allows you to make calls and send messages using your data connection instead of munching through calls and minutes included in your contract.