Apple has failed to issue a security patch for a vulnerability that could allow criminals to take control of iPhones using text messages, say security researchers.
Apple was believed to be working on a patch after researchers notified the firm of a vulnerability in the way the iPhone handles text messages.
But the researchers, Charlie Miller and Collin Mulliner, said Apple had not released a fix ahead of their demonstration of how the flaw could be exploited at the Black Hat security conference in Las Vegas.
Charlie Miller and Collin Mulliner had agreed to keep details of the flaw under wraps until the Black Hat conference this week.
Earlier this month, Miller demonstrated at the Syscan security conference in Singapore of how to use the vulnerability to disconnect an iPhone from the network, but he gave no details of the attack method.
After the Black Hat demonstration, Miller and Mulliner said hackers could develop software to exploit the vulnerability, putting more than 20 million iPhone users at risk.
They warned that once exploited, the iPhone flaw could be used to take control of the devices dialling, web browsing and texting functions.
Apple has not responded to requests for information about the iPhone vulnerability.