Apple users are being advised to update their software immediately after the company was notified of a security flaw.
Affecting the iPhone, iPad, Mac and Smart Watch products, it reportedly allowed them to be exploited by spyware.
The tool, called Pegasus, is said to be able to open and copy text messages, videos, photos and web activity including passwords.
Researchers say it was used on a phone belonging to a Saudi activist.
To combat the attack Apple has updated its software, with many devices automatically iOS 14.8 overnight.
It's thought to be the first time a so-called 'ero-click' exploit has been caught and analysed.