Apple has railed against the practice of jailbreaking its phones in a filing to the US Copyright Office, which is considering a request from the Electronic Frontier Foundation to legalise the widespread practice.

If Apple's statements are accurate, jailbreaking could allow hackers access to low-level sections of a phone's operating system which controls its connection to cell towers. That would enable a hacker to crash a tower entirely. "Taking control of the BBP software would be much the equivalent of getting inside the firewall of a corporate computer - to potentially catastrophic result", says Apple.

The Electronic Frontier Foundation wants to legitimise the practice so that Apple's lockdown on the device is removed. Jailbreaking allows anyone to install whatever app they choose on the handset, whether or not its installation has been sanctioned by the company.

The EFF attorney who made the request, Fred von Lohmann, has called Apple's claims preposterous - "As far as I know, nothing like that has ever happened". He also added that if Apple's claims were realistic, then Google's Android handsets would be just as much of a danger as an unlocked iPhone.