Apple says it is trying to fix a major glitch within its latest Mac operating system.
The bug in MacOS High Sierra means anyone can gain entry to the computer without a password, giving them administrator rights.
In a statement, Apple said: "We are working on a software update to address this issue."
The problem was made public by Turkish developer Lemi Ergin, who found by typing in the username "root", not entering a password and hitting "enter" a few times, he could get unrestricted access to the system.
— Lemi Orhan Ergin (@lemiorhan) November 28, 2017
He described it as a "huge security issue", adding the result was "unbelievable".
In response, the Apple Support Twitter account asked him to direct message them, saying: "Let's take a closer look at what's happening together."
A workaround has been announced by Apple while it works on the problem.
The company said on its website: "Setting a root password prevents unauthorised access to your Mac.
Let's take a closer look at what's happening together. Send us a DM that includes your Mac model along with your macOS version. We'll meet up with you there. https://t.co/GDrqU22YpT
— Apple Support (@AppleSupport) November 28, 2017
"To enable the Root User and set a password, please follow the instructions here.
"If a Root User is already enabled, to ensure a blank password is not set, please follow the instructions from the 'Change the root password' section."
The other option for worried users is to make sure they do not let their computer out of their sight and to make sure they update their system when prompted.