Unlocked iPhones may become inoperable, according to an Apple warning that comes in response to the growing number of third-party hacks for its high-profile handset. UPDATE: Apple iPhone unlock hackers vow to fight Apple's policy of killing hacked iPhones.

"Apple has discovered that many of the unauthorised iPhone unlocking programs available on the internet cause irreparable damage to the iPhone's software, which will likely result in the modified iPhone becoming permanently inoperable when a future Apple-supplied iPhone software update is installed," Apple said.

Unlocking the iPhone is a process that hackers have developed to allow the device to work with SIM cards from carriers other than AT&T Wireless, Apple's preferred carrier in the US. The applications and instructions developed by hackers over the past couple of months are freely available on the internet, but users may wish they waited.

The first hint that Apple would take a more aggressive stance towards unlocking hacks came last week during the company's London press event to announce the UK release ship date for the iPhone. Asked what Apple was doing to stop people from unlocking their phones, CEO Steve Jobs called it "a cat and mouse game".

"I'm not sure if we are the cat or the mouse. People will try to break in, and it's our job to stop them breaking in," he added.

Apple made it very clear that it would not be responsible for any damage caused by the installation of third-party unlocking software.

"Users who make unauthorised modifications to the software on their iPhone violate their iPhone software licence agreement and void their warranty," Apple said. "The permanent inability to use an iPhone due to installing unlocking software is not covered under the iPhone's warranty."

In the UK, analysts have warned that iPhone owners who attempt to unlock the handset and use it with operators other than O2 may face huge monthly bills.

"At the moment, as a consumer, you need to be very careful about unlocking the iPhone, and know how you want to use it," said Gartner's Carolina Milanesi. "If you unlock it, you are not going to have a flat rate, and you will not have access to the 7,500 hotpots."

See also:

How to unlock an Apple iPhone for free

O2's UK iPhone sacrifices revealed

Top 25 requests for the UK Apple iPhone

Apple iPhone: the definitive review

The 10 most ridiculous iPhone stories so far

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