Mexico is to crack down on criminals who use mobile phones to contact kidnap victims' families to demand a ransom. The central American country is to fingerprint anyone who buys a new mobile phone and store their details on a national register.

A law passed yesterday and that will come into force in April will require mobile phone operators in Mexico to build up a database of their customers' fingerprints.

Unlike the UK and the US, where mobile phones are generally bought on a contract, in Mexico, most handsets are pay-as-you-go models, meaning there's no ongoing record of the customer, no SIM card associated with the handset and no reason to have a verified home address for them.

Kidnapping is big business in Mexico, with hundreds of people abducted each year. Mobile phones are a popular and convenient way for kidnappers to contact a victim's relatives and demand money. Using a disposable SIM card and cheap handset, they can make the call and, once their demands have been met, dump the evidence.

There are approximately 80 million mobile phones in Mexico (a country of some 109 million citizens), most of which are prepay phones. At present, these can be topped up with a modest number of credits instore, explains Reuters, without the customer needing to produce any form of identification. As in the UK, top-up vouchers can then be bought at other high street outlets and stalls.

The new law will see mobile phone vendors legally obliged to collect fingerprints of all new subscribers and to retain details of calls made and text messages sent and received on the handsets for a year. The data will be stored on a central government database. Mexican lawmakers say the database will only be accessed when actively seeking evidence of a specific crime.

America Movil, Mexico's largest mobile phone operator, believes handset tracking would be a more useful move if the bill is to be effective in clamping down on mobile phone use in kidnaps. This, however, would invite further claims of privacy invasion.

Mexican mobile phone operators will have a year to comply with the new law once it comes effective, while consumers will be legally obliged to report stolen or missing handsets immediately.