As the fall-out from the News of the World scandal continues, many sources continue to inaccurately refer to “mobile phone hacking”. The truth (as far as is known) was that it was the voicemail of the mobile phone that was hacked rather than the phone itself. There are two ways to do this – the first is to simply guess the PIN of the voicemail and the second is to use Caller ID spoofing.
In the mid-2000s, most mobile phone voicemail systems were poorly protected as they typically came with a default PIN which was often easily guessed and only varied according to the mobile phone company. Most users didn’t bother to change the PIN. Say the phone was on Orange, then the default PIN was 1234. If it was Vodafone, then 0000. Typically, the villain then makes two simultaneous calls to the victim. One will be picked up, the other will go to voicemail. By then pressing “*” or “#” while listening to the voicemail prompts, the individual can gain access to the voicemail system using the default PIN. Computeractive has article covering this scenario and how, in theory, it would be harder (but not impossible) to take this approach today.
As for Caller ID spoofing, this technique makes a call look like it’s coming from a different number than it actually is. It can be used legally to make someone calling from a mobile to actually appear to be coming from a company office, so that the person’s mobile number is not divulged. However, in some instances it has been used to gain access to voicemail boxes as many voicemail systems do not ask for further identification if the system recognises the inbound Caller ID as one of its own. PC Mag and c|net have short articles on how this is done and worryingly, this is still a threat. The Wall Street Journal covered the problem in 2010 before the current scandal broke.
It would appear that the best protection to both these attacks is (a) to change your PIN on your voicemail and (b) require your PIN even when calling from your own mobile phone. That way, even if your Caller ID is spoofed, the caller can’t get in without knowing your PIN.