Facebook-owned WhatsApp has criticised Apple over a new technology that finds child sexual abuse material (CSAM) on users' devices as it can be used by authoritarian governments to spy on citizens.

The technology will search for matches of known CSAM before the image is stored onto iCloud Photos.

Apple said that new versions of iOS and iPadOS – due to be released later this year – will have "new applications of cryptography to help limit the spread of CSAM online, while designing for user privacy".

The system will report a match which is then reviewed by a human. Steps can then be taken to disable a user's account and report the matter to the law enforcement agencies.

However, WhatsApp head Will Cathcart said he was very concerned over Apple's move. “ I think this is the wrong approach and a setback for people’s privacy all over the world,” he tweeted.

“People have asked if we’ll adopt the system for WhatsApp. The answer is no.”

“Apple has for long needed more to fight CSAM but the approach they are taking introduces something very concerning with the world,” Cathcart added. 

He said the system "could very easily be used to scan private content for anything they or a government decides it wants to control. Countries where iPhones are sold will have different definitions on what is acceptable".

He pointed out that the WhatsApp's system to tackle child sexual abuse material has reported more than 400,000 cases to the US National Center for Missing and Exploited Children without breaking encryption and upholding the privacy of users. 

But Apple says that the new technology offers "significant" privacy benefits over existing techniques – as Apple only learns about users' photos if they have a collection of known child sex abuse material in their iCloud account.

According to BBC, the Electronic Frontier Foundation, a digital rights group, has also criticised the move, labelling it "a fully-built system just waiting for external pressure to make the slightest change".  But some politicians have welcomed Apple's development.

Sajid Javid, UK Health Secretary, said it was time for others, especially Facebook, to follow suit.

US Senator Richard Blumenthal also praised Apple's move, calling it a "welcome, innovative and bold step".

"This shows that we can protect children and our fundamental privacy rights," he added.