How easy is it to hack a mobile phone voicemail?

The phone hacking scandal has been dominating headlines in most of the papers for the past few days. What's missing in a lot of the coverage is seemingly quite important: just how do you hack a voicemail and how can you protect against it? We look at just how easy it is (or was) to hack into a voicemail and also provide you with some tips for securing your voicemail against hackers.

When someone says the word 'hacker' it might conjure up the image of a cunning tech-wizard doing all sorts of clever trickery. When it comes to phone hacking, a lot of the time this couldn't be further from the truth.

In some cases the allegations against the News of the World date back quite a few years (to the early 2000s) and systems and technologies have changed a lot since then.

In the past, many mobile phones came with 'default' PINs for accessing voicemails - the idea being that people would change the default PIN to something unique. If they didn't, the default PIN was all someone would need to get into a voicemail inbox. Needless to say, hacking in these days was shockingly simple.

With that in mind, here's a step-by-step guide for ‘hacking in the past': call the person you want to 'hack' on one phone, then with the line engaged call them on another phone to go through to their voicemail. Press the '*' key to access the voicemail menu and enter their PIN number. As each network had its own 'default' PIN (1234, 5555, 0000, etc.) hacking into a voicemail account wasn't that challenging.

Things have now changed. Mobile phone operators ditched default pins years ago and in order to get access to a voicemail a user will have to set up their own PIN. For clarity, we checked with the major mobile operators to find out how they currently run their voicemail systems. Here's a selection of their policies:

• Orange informed us that in order to access voicemail remotely a personalised PIN must have been setup by the user. The company also said that 'easy to guess PINs' that contain repeated numbers (2222) or consecutive numbers (5678) cannot be used.

• Three allows for a PIN that's up to eight digits long. When first setting up a voicemail a user will be asked to choose a PIN. Remote voicemail access from another phone won't be possible until a unique PIN has been setup by the user.

• Vodafone said that to get access to voicemail messages using another phone a user will need to call a 'generic number' (+447836 121 121) and then follow the steps to setup a PIN code.

So how can a devious hacker get access to Sienna Miller's voicemail in this day and age? Well, on some networks a hacker would need to call the phone number in question and hope it is either engaged or it isn't answered, then enter/guess the PIN to gain access.

On other networks it is made much easier by the presence of a generic voicemail number (as on Vodafone) that asks the hacker to enter the phone number and related PIN. The problem being, both methods require that the hacker knows, or can guess, the PIN.

After all that, the issue still remains. While voicemails can still be accessed remotely, there will always be the danger that people can either guess or illegally obtain PIN numbers. The solution? Networks should stop remote voicemail access. If you're worried, the best advice we can give is to make your PIN really hard to guess, or turn your voicemail service off completely.