Apple customers have discovered a significant security flaw in the latest version of the operating system for Mac computers that allows anyone to log in without a password, potentially making private user data vulnerable.

The issue, discovered in the MacOS High Sierra operating system for laptops and desktops that was released in September, allows people to enter the word "root" when prompted for a username, and provide no password when logging on to the device. The glitch allows anyone to access the file system for a Mac, exposing private documents on that particular computer. One user reported the ability to also access the computer using the root login remotely.

The glitch is a rare and potentially embarrassing failure for Apple, whose software is generally known for being less prone to hacking and malware infections than Windows software from Microsoft. The previous version of the operating system didn't appear to be affected by the bug.

"A password prompt that authenticates as root with an empty password would be a black eye for any OS. Never mind one from a security and privacy-conscious company such as Apple," Steve Troughton-Smith, a Mac software developer, wrote on Twitter.

Tests of the flaw indicate that it could be used to alter a user's system settings that normally require a chosen username and password. Some settings include changing key security preferences -- like enabling or disabling a computer's firewall or storage drive encryption.

The flaw was publicised Tuesday on Twitter by Lemi Orhan Ergin, a software engineer based in Turkey. Edward Snowden, a key voice in the information security community after being the centre of many years of National Security Agency leaks, commented on the disclosure. "Imagine a locked door, but if you just keep trying the handle, it says 'oh well' and lets you in without a key," he wrote on Twitter.

Overnight, Apple released a security update for the software. The fix is available for download in the App Store and later in the day will be automatically installed on all systems running the latest version (10.13.1) of macOS High Sierra.

"Security is a top priority for every Apple product, and regrettably we stumbled with this release of macOS," Apple said in a statement. "We greatly regret this error and we apologise to all Mac users." Apple said it's auditing its development processes to help prevent such a situation from happening again.

Bloomberg