The privacy of your next mobile phone conversation could be in doubt, as a German computer scientist has cracked the the GSM algorithm used to keep around 80% of the world's mobile phone conversations private.

Karsten Nohl and his team of 24 hackers have been working on decoding the GSM security since August and have now published the code online, supposedly meaning that anyone with a laptop with two network cards "could be recording phone calls within 15 minutes".

The GSM security algorithm sees phones and base stations changing frequencies constantly to avoid interception but is 21-years-old. A newer system was developed in 2007 but it's said that most network operators have not upgraded.

Nohl told The Guardian he had deceiphered the code in order to force an upgrade: "This shows that existing GSM security is inadequate".

The GSM Association says: "We consider this research, which appears to be motivated in part by commercial considerations, to be a long way from being a practical attack on GSM".