Less than 24 hours after Apple had revealed its preview of iPhone OS 4.0 and made it available to developers, hackers revealed they had successfully manage to run an unauthorized VNC client on the mobile operating system.

A hacker from the iPhone Dev Team who goes by the handle MuscleNerd uploaded on Friday a video of an iPhone 3GS running the iPhone OS 4 beta, as well as Veency, which is virtual network computing software available as an unauthorized application for the iPhone. To run software like Veency, an iPhone must be "jailbroken," which is the name given to a process that allows users to run unauthorized code on Apple's handset.

He noted via his Twitter account that Apple's pre-release betas are "very" buggy, and cautioned users not to test it on their own iPhone.

The hacker also took issue with Apple's claim made Thursday that hardware restrictions have prevented multitasking from being enabled on older iPhone hardware. In addition to existing unauthorized jailbreak solutions for multitasking, the hacking community has also released software to enable MMS functionality on the first-generation iPhone.

The latest development is by no means confirmation that any jailbreaking methods will work with iPhone OS 4.0 when it ships. It's likely that Apple will make changes to thwart those exploits before the software update is made available this summer.

It's also expected that Apple will build in new hardware security features in its next-generation iPhone, due to be announced this summer. Late last year, Apple became more aggressive against jailbreak attempts when it quietly updated the BootROM in the iPhone 3GS to thwart potential hackers. It marked the first time ever that the handset maker had modified its hardware in the middle of a product line, without a new model released.

Earlier this week, MuscleNerd demoed a new jailbreak method that was said to work with Apple's iPad, iPhone 3GS and third-generation iPod touch. The software has not yet been released publicly, but could allow users of the latest hardware revision of the iPhone 3GS to unlock their handset for use on alternative carriers. There is no need to unlock the iPad, which does not ship with a carrier lock.

The warranty-voiding jailbreak process can also allow users to run software Apple does not allow. Hackers have created their own custom applications that Apple might not allow in the App Store. Jailbreaking can also be used to pirate App Store software, one major reason why Apple has fought the practice.