Grant Paul, who develops software for Apple's iOS operating system, posted photos on his Twitter page of a 'jailbroken' iPhone 5.
Apple ships its iPhones and other mobile devices with restrictions that only allow Apple-approved software to be installed.
Tweet heard 'round the world: Hacker Grant Paul posted this screen shot of his iPhone 5 running Cydia, an app available only on hacked devices, as proof he had 'jailbroken' his new phone
Instructions for stable 'jailbreaks' are posted online, which allow normal users to free their phones of Apple's restrictions.
Tech news site The Next Web reports that Mr Paul's hack of the new phone is remarkably fast.
The iPhone 5 runs on Apple's new iOS 6 operating system, which does not have the same security flaws as previous versions of the software.
Other hackers have also found cracks to jailbreak older devices running the new operating system.
Already hacked: Less than eight hours after throngs of fans rushed Apple stores to buy the new iPhone on Friday, Mr Grant hacked the new device
Proof: Mr Grant also posted these two photos to quiet skeptics who said he hadn't actually cracked the new phone. Most in the tech community accepted these images as evidence the device had been 'jailbroken'
Apple fans lined up around the world to have the first chance at buying the iPhone 5 at 8am on Friday.
At 3.49pm on Friday, Mr Paul tweeted a photo of an iPhone5 screenshot that included Cydia, the app used to download non-Apple-approved software on jailbroken iPhones.
The implication of the photo was that Mr Paul had been able to download Cydia to his iPhone 5 only because he was successfully able to hack it.
He celebrated the remarkable achievement with an understated tweet: 'Taller screens like Cydia too. :)'
As skeptics weighed in, Mr Paul posted a screenshot of the Cydia home page and then a photo of his phone with Cydia on it.
The tech community has largely accepted the pictures as proof that the iPhone 5 has successfully been cracked.