Apple releases security update for macOS High Sierra 10.13.1
The update addresses a serious security vulnerability that, in certain circumstances, could enable an attacker to gain full access to your Mac and everything on it without a password.
Apple has advised that users of macOS Sierra 10.12.6 and earlier versions are not impacted by the vulnerability that the security update addresses.
Further information is provided by Apple at https://support.apple.com/en-us/HT208315, including links to advice about 'How to update the software on your Mac' and find your macOS version and build number.
Sierra macOS users can also configure their computer to 'Install system data files and security updates automatically'. Information on how to do this is provided at https://support.apple.com/kb/PH25532?locale=en_US
Stay Smart Online recommends that you always turn on automatic security updates on your computing devices.