The iOS platform has a potentially hazardous flaw in its security that could leave users exposed, a leading web security firm claims.
Symantec believes that the threat which it has identified is only theoretical since it has not yet been exploited, but has urged Apple to apply a fix quickly so that users are not affected.
Apple has confirmed that it has been informed of the flaw and that it is taking steps to look into it.
The exploit hinges on the fact that the Safari browser loads PDF files automatically, giving hackers a window in which infected files might be transmitted to an iPhone unhindered.
Security expert Graham Cluley told BBC Online: "It uses the same tricks as you do when jailbreaking.
"We always thought that Apple's Mobile Safari would be the main vulnerability. At present, we have yet to see any of these exploits out in the wild, but it is only a matter of time."
The problem can apparently only be remedied if a user is willing to jailbreak their iPhone.
Mr Cluley added: "I personally wouldn't want to jailbreak my phone to get the fix. Right now, it's all eyes on Apple who we hope are going to fix this problem as soon as possible.
"Historically, Apple have been slow to fix problems on their Mobile browser. This has been a concern of ours in the past and continues to be."