Update: Apple has confirmed a fix in iOS 7.1.2. An issue with how iOS 7 handled telephony features while in Airplane Mode caused the bug, but the problem has now been addressed.

Apple's iOS 7 mobile operating system is vulnerable to another attack that allows the lock screen to be bypassed, allowing anyone to access the most recently used application.

The bug takes just seconds to exploit but depending on what the most recently used application was, it is still a major privacy concern. A video demonstrating the bug explains that the Notification Centre and Control Centre need to be accessible from the lock screen and the iPhone must have a missed call.

By pulling up the Control Centre and putting the iPhone into Airplane Mode and then pulling down the Notification Centre and tapping on the missed call it is possible to access the most recently used application.

All iPhones running iOS 7 are thought to be vulnerable to attack. Concerned users should go to Settings and disable lock-screen access to the Notification Centre until Apple can release a bug-fix patch for the flaw. It is likely that the bug will be fixed in the next version of Apple's mobile operating system, iOS 8 .

The lock-screen is a common feature of smartphones, with passwords, PINs and patterns all common. Some recent Android handsets have used facial recognition and Apple's iPhone 5S can scan fingerprints. Flaws in both passcode lock screens and fingerprint and facial recognition systems have been uncovered for both Android and iOS.