For millions of people, mobile phones have become essential for everyday life.

But just how secure are our supposedly private calls, texts and voicemails?

The latest alleged high profile security breach, reportedly involving the phones of royal officials and other public figures, centres on the illegal accessing of voicemail messages.

Hacking into voicemails on a mobile phone is a relatively straightforward process if the user has not changed their "pin code", according to industry experts.

Hackers can obtain the number which allows for remote access to the voicemail system and, by inputting the default code or other commonly used numbers, can gain access to messages left by other callers.

It is a "weakness in the system" allowing snoopers access to information much more easily than hacking into direct communications such as live mobile conversations, according to industry body the Telecommunications UK Fraud Forum.

Chief executive of Tuff, Jack Wraith, said: "It highlights the customers' use of modern devices which give them all the functionality and facilities without them standing back and asking 'what am I doing here, and what's the increased risk to me and my information?'.

"Whenever you put technology in the hands of the user, there is always the potential that some users will find some way around the system in order to exploit it."

He continued: "When you set up a voicemail facility there is an option to set your own pin (personal identification number) and one should be encouraged to do that."

He also said it was important when leaving a message not to include information - for example relating to business activity - which might be considered sensitive.

Actual mobile telephone conversations are another matter.

Both the Prince of Wales and his then wife Diana had to endure the publication of the contents of private mobile conversations during the dying days of their turbulent marriage.

The Prince's call, to his then mistress Camilla Parker Bowles, was said at the time to have been recorded by a radio enthusiast using a scanning device, although doubts were later raised about exactly how the call came to be traced.

Because of the very latest digital technology, which sees actual phone conversations encrypted between the phone and the nearest network point, it is much harder to hack into direct calls, Mr Wraith said.