Security experts are warning of a serious vulnerability in the iPhone that could allow hackers to remotely execute code on the device.

Security researcher Charlie Miller announced the findings at the SyScan conference in Singapore yesterday. He is now reportedly working with Apple to get the problem fixed as soon as possible.

Patrick Runald, chief security advisor at Finnish web security firm F-Secure, argued on the firm's blog that the vulnerability, which exploits a weakness in the way the device deals with text messages, is "as bad as it gets".

"The vulnerability seems to allow unsigned code to run, which circumvents a core part of iPhone's security model," he wrote. "It's usually only able to run signed code, i.e. apps that have been approved by Apple. No user interaction is required, which is unlike current mobile malware."

The vulnerability could enable hackers to remotely turn on the GPS function to monitor the handset's location, or turn the microphone on to listen in on conversations, Miller is reported as saying.

Apple will be hoping it finds a fix for the vulnerability before Miller discusses the flaw in greater detail at a planned Black Hat presentation.

It has been a bad week for the iPhone. Supplies have been running out in parts of the US, and the blogosphere has been awash with claims that the new 3GS model is prone to overheating.