Intego, billed as the Mac security specialists, has warned of a potential flaw in Apple's mobile operating system, which powers the iPhone.

"An iPhone bug has been reported which allows users to bypass a locked iPhone and access certain features," Intego warns on The Mac Security Blog.

"This occurs when someone attempts to make an emergency phone call, then quickly presses the hardware lock button."

Intego highlights a MacRumors forum posting from jordand321, based in Wellington, New Zealand, under the post heading: 'iOS 4.1 Security Issue - Bypassing the Lock Screen to Make Calls.'

"When you iPhone is locked with a passcode tap Emergency Call, then enter a non-emergency number such as ###," notes jordand321. "Next tap the call button and immediately hit the lock button. It should open up the Phone app where you can see all your contacts, call any number, etc."

Apple iPhone 4

While jordand321's iPhone is jailbroken, MacRumors forum members confirm the bug exists with all iPhone's running iOS 4.1.

Apple appears to working on a fix for the bug. Intego adds: "Apparently, it is not, however, present in the latest beta version of iOS 4.2, so Apple had either already found the bug and corrected it, or corrected the root cause of the issue when fixing other problems in iOS."

iOS 4.2 will be released in November, and include an update for Apple's iPad.