The security flaw came to light nine days ago as the website www.jailbreakme.com released code that Apple customers can use to modify the iOS operating system that runs those devices through a process known as "jail breaking."

With this flaw, malicious hackers could have remotely controlled iPhones, iPads and iPod Touches after tricking the user to open a malicious PDF file.

Some Apple customers choose to jail break their devices so they can download and run applications that are not approved by Apple or use iPhone phones on networks of carriers that are not approved by Apple.

The jailbreaking code exploited a vulnerability in iOS that had not previously been disclosed. Its release gave criminal hackers a blueprint they could use to build malicious software that would exploit the vulnerability.

However, Apple released a new iOS update that patches the PDF flaw. The iOS 4.3.4 update fixes a vulnerability in the CoreGraphics frameworks that resulted in problems in the way PDF files were being handled.

The update is available for iPhone 3GS and iPhone 4 running iOS 3.0 and higher, third-generation iPods with iOS 3.1 and higher, and iPads with iOS 3.2 and higher.