Jonathan Zdziarski, an iOS exploitation expert, warns the public that users of Apple's iPhone can be surveilled through their own phones.

Zdziarski said there are undocumented forensic services and surveillance mechanisms within iOS, or the operating system that runs Apple's popular iPhones. The researcher noted one of these services, the bypass back-up encryption, copies more personal data than it should. 

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He claims these backdoor tools can allow anyone to get a hold of sensitive data including photos, contacts and locations.

Even though he doesn't have any firm proof, he said the National Security Agency (NSA) might have used this method to secretly access information in iPhones.

In his paper, Zdziarski said the exploitation of these features requires the iPhone be paired with computer. This pairing results in a file being stored in both the phone and the PC.

The paired file then can be used to download, install and manipulate data and applications on the target iPhone. 

"Anyone who retrieved that file could siphon off all kinds of data from an iPhone," Zdziarski said.

He noted, however, that this feature is "good news for the 'good' cops, who do crazy things like get warrants, [but] it's very bad for anyone who is targeted by spy agencies or malicious hackers looking to snoop on their data."

Apple has not responded to this spying issue.

It has, however, defended the bypass back-up, saying the purpose of this service is to allow IT departments and store assistants to easily manage iPhones.