Hassell and Macaulay built a proof-of-concept for that spoofing attack using a fake sign-in for the Skype Android app.

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The UK is already investigating claims that six of those involved in the attack were travelling on fake British passports.

BBC: Urgent question

But the trick could be scaled up to hundreds or thousands of fake signals, much like a denial-of-service attack that uses thousands of computers to choke a website with a flood of fraudulent requests for information, Costin says.

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