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All the data on some of the tablets and phones seized as evidence is being wiped out, remotely, while they are in police custody, the ����ý has learned.

Cambridgeshire, Derbyshire, Nottingham and Durham police all told ����ý News handsets had been remotely "wiped".

And Dorset police said this had happened to six of the seized devices it had in custody, within one year.

The technology used was designed to allow owners to remove sensitive data from their phones if they are stolen.

"If a device has a signal, in theory it is possible to wipe it remotely," said Ken Munro, a digital forensics expert with Pen Test Partners.

Romance fraud

A spokeswoman for Dorset police told the ����ý: "There were six incidents, but we don't know how people wiped them.

"We have cases where phones get seized, and they are not necessarily taken from an arrested person - but we don't know the details of these cases as there is not a reason to keep records of this," she added.

A spokeswoman for Derbyshire police confirmed that the force had had one incident of a device being remotely wiped while in police custody.

"We can't share many details about it, but the case concerned romance fraud, and a phone involved with the investigation was remotely wiped," she said.

"It did not impact upon the investigation, and we went on to secure a conviction," she added.

Meanwhile Cleveland police told the ����ý that it too had had a case of a phone that had been wiped but it was not clear "whether it was wiped prior to coming into police hands".

Asked whether the police felt that the issue had damaged their investigation, the spokeswoman said: "We don't know because we don't know what was on the phone."

Other police forces affected by the issue include:

Microwave help

Mr Munro, who analyses hundreds of laptops, tablets, phones and other devices for corporate clients, said: "When we seize a device for digital forensics, we put it immediately into a radio-frequency shielded bag, which prevents any signals from getting through.

"If we can't get to the scene within an hour, we tell the client to pop it in a microwave oven.

"The microwave is reasonably effective as a shield against mobile or tablet signals - just don't turn it on."

SecureDrives, which develops hard drives for the military, is releasing one next year that can be physically destroyed just by sending a text message.

The hard drive -which will cost more than £1,000 - is also immune to the radio-frequency blocking bags.

"The hard drive is constantly looking for GSM [Global System for Mobile Communications] signals, if it is starved of them it it would destroy itself. It would see such a bag as a threat," said James Little, head of sales at SecureDrives.