iOS devices offer three authentication methods to access the device with varying levels of security for each method.
Swipe: This is the default method which requires the user to do a swiping motion to unlock the screen to access the device. It is not meant to secure the device but to prevent accidentally pressing buttons on the device.
PIN: This method allows the user to choose a PIN between 4-16 digits long. The longer the PIN the more secure the device will be. Choosing simple PINs of 1234 or similar should be avoided as the device will not be very secure. This is a medium to high security method of device authentication.
Password: This method allows the user to choose a password that has at least 4 letters or numbers long. The longer the password the more secure the device will be. Choosing a simple password should be avoided as those passwords might be easily guessed.
In iOS 6.1 a bug was discovered that allows the screen lock to be bypassed thereby allowing someone to access the data without having the passcode. This means that even a strong passcode could be bypassed in order to gain access to the data stored on the device [3].