Apple has issued an urgent waring to all iPhone users to update their phones to stop dangerous spyware infecting mobiles.

The urgent security software update was sent out to fix an issue which lets hackers access devices through iMessage - even if users do not open the link or file.

Apple said the issue affects all iPhones, iPads and Macs and issued the security update in response to a "maliciously crafted" PDF file.

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The security flaw allows attackers to deploy what’s called a ‘zero-click exploit’ that can run silently without the owner of the device having to click on a suspect link or open a document.

Once the infected files – in this case, PDF documents disguised as GIFs – are on a device, Pegasus spyware is silently installed.

Once the spyware is on a device, the attackers can silently copy and steal the messages sent and received on the phone, use the camera to secretly film the phone’s owner, and eavesdrop via the microphone.

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While it’s very unlikely that ordinary users’ Apple devices will be targeted by Pegasus spyware, the vulnerability the researchers found has worried security experts.

Apple’s head of security, Ivan Krstić, said: "Attacks like the ones described are highly sophisticated, cost millions of dollars to develop, often have a short shelf life, and are used to target specific individuals.

"While that means they are not a threat to the overwhelming majority of our users, we continue to work tirelessly to defend all our customers, and we are constantly adding new protections for their devices and data.

"If you haven’t yet updated your Apple devices this week, you should check for the update and run it as soon as possible."

An update for the vulnerability was pushed out on September, 13 by Apple, which updates iPhones to iOS 14.8, and iPads to iPadOS 14.8.

Apple Watches are updated to watchOS 7.6.2, while Macs running the current Big Sur version of macOS are updated to Big Sur 11.6.

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