Most worryingly, said Mr Steggles, it was possible to extract the temporary files that Microsoft's Internet Explorer browser uses to keep track of what people do when they are using the web.

With a little work, it was possible to reconstruct almost everything that some users did online, and to grab cookies and login details for sites they visited.

"With not a massive amount of work we could go in there and help ourselves to whatever we want," he told the BBC website.

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