The phone hacking scandal at The News of the World made global headlines when it was revealed that the newspaper had been using private investigators to hack into the voicemails of not only celebrities, but also murder victims and the families of people killed in the 7 July bombings on the London Underground.

The actions have already caused the closure of the paper and the arrest of its former editor as well as calling into question his previous role as Prime Minister David Cameron's communications director, but the scandal has also highlighed just how easy it is to hack into mobile phone accounts. 

Most mobile networks offer a service where you can use a PIN code to access your mobile's voicemails by calling it from another phone - handy for when you've left it at home or the battery dies when you're out and about. A default PIN code, such as 0000 or 1234 is usually set and, as many people rarely use this service, they never get round to changing the number. That means that any unscrupulous characters can listen to your voicemails by calling your phone (providing that there's no answer) and make an educated guess at your PIN. 

Phone hacking is illegal, but that's never stopped a criminal before, so whether you're on Vodafone, Orange, O2, Three, T-Mobile, Tesco Mobile or Virgin Mobile, Pocket-lint spoke to the mobile networks to find out how to keep your voicemail box safe.

Orange

Orange was keen to point out that it takes the security of its customers' personal information very seriously and has plenty of measures in place to keep it safe. The company spokesperson told Pocket-lint:

"Mobile phone calls and texts are protected by encryption technology and we provide customers with controls such as the ability to set up PIN access to protect their voicemail. Orange is focused on ensuring the best possible security for all our services and offers a number of preventative measures to help protect our customer's voicemails. We regularly review our security controls to ensure they are effective against current and emerging threats and adapt them where appropriate."

The measures that Orange has in place include text alerts to let you know when a voicemail PIN has been set up or changed, as well as systems to prevent you from choosing any daft PIN codes like 1111. Remote access to voicemail is switched off by default so you'll need a verified PIN to get into it from the start. If you need more help, then Orange's customer service teams are trained on all security procedures and there's also plenty of information on the website. 

In order to change your Orange PIN code, you'll need to follow these steps:

1. Press and hold 1 to access your Answer Phone menu.
2. Press 3 for settings and features.
3. Press 3 to set your PIN. This needs to be between four and ten digits long and you'll be prevented from entering obvious codes like 1111 or 1234.

Although there's plenty of information on the website, Orange told us that: 

"There are currently no plans to pro-actively contact customers on this topic, however we certainly would remind them if they call a call-centre, are in-store or comment online and have questions about security."

O2

According to a spokesperson at O2, the company requires a personalised PIN code from the off. They told us:

"O2 Customers are required to set a personalised PIN for their voicemail before messages can be retrieved remotely. We also recommend that our customers enable PIN protection for direct retrieval to ensure no one else can access their messages even if they get hold of their handset. Of course - customers should also ensure they choose a PIN that is not easy to guess by others."

So, O2's advice is to set up a PIN as soon as you can. If you can't remember whether you've done it already or no, then we suggest that you go and do it now.

In order to change your O2 PIN code you'll need to do the following:

1. Dial 901
2. Press * for greetings and mailbox settings and then 4
3. Follow the prompts

Although the O2 didn't mention anything about contacting customers directly to reiterate the threat posed by phone hackers, the brand has produced an O2 Guru TV video on how to keep your voicemail secure.

Vodafone

Vodafone recognised the importance of voicemail security when phone hacking hit the headlines several years ago and has had measures in place ever since. A spokesperson at Vodafone told us:

"Customers can only access their voicemail from their own phone or from another phone by using a pre-set PIN code which they themselves have requested and set from their phone or which is a number generated at random by our system.  If attempts are made to access voicemail with a different PIN, the customer receives a text to alert them.

"Immediately after the first reports of phone hacking in 2006 by or on behalf of journalists, we put in place additional measures to protect our customers' privacy specifically designed to prevent the kind of unlawful intrusions that may have been committed by others in the past.  We are confident that our voicemail system is secure."

In order to set to set or change your Vodafone voicemail PIN you'll need to do the following:

1. Call 121 SEND and wait for the main menu: 
2. Press 4 then 2 to access the security settings
3. You'll then be offered a range of options to change the security settings including the security level and changing your current PIN. Security codes can be any four-digit number, but repeated or sequential numbers (such as 1111, 1234 or 4321) won't be accepted.

Three

Three's voicemail can't be accessed using a default passcode and the brand highlights the importance of choosing a PIN that isn't too easy to guess. A spokesperson told us:

"There is no default PIN number on Three - in order to access your voicemail remotely, you need to set up your on PIN number. This is a system that has been in place for some time. Don't use your birthday and don't choose anything obvious like 1234 as these won't take long to crack. We have guidelines on security on our website and we've been responding to lots of telephone queries following the recent events in the news."

In order to change your Three PIN, follow these steps:

1. Dial 123 on your Three phone to access your voicemail
2. Select option 4 to change your mail settings
3. Select option 2 to manage your log-in options
4. Select option 1 to change your PIN
5. Enter your new PIN followed by #. Your PIN code must be between four and eight characters long and different from your previous PIN.

T-Mobile

To set up or change your PIN code for your T-Mobile voicemail, you'll need to:

1. Access your voicemail as normal
2. Select option 2 then 1
3. Enter a four-digit PIN of your choice, then press #.

Tesco Mobile

According to the Tesco Mobile website, the network's voicemail service has a default PIN code of 8705, so it's a good idea to sort this out asap. To change your Tesco Mobile PIN, here's what you need to do:

1. Call 905 from your mobile
2. Press the * key
3. Select option four from the main menu options4. Follow the prompts.

Virgin Mobile

For Virgin Mobile, the process for setting your PIN number varies depending on the handset. There is a default code, although it's only given to customers who require it (presumably it's nothing as obvious as 0000). In order to change your PIN, Virgin Mobile told us that you should:

1. Dial 222 from handset to set up voicemail
2. If already set up, hold down 1 on handset to enter voicemail
3. Enter current PIN
4. Follow voice prompts to change settings (including PIN)

Have you ever had your phone hacked? Let us know in the comments box below.