Apple’s newest operating system has a serious vulnerability that can allow someone else to logon to your Mac. Here’s what to do:
First, see if you are vulnerable. Click on the apple symbol on the top left of your screen, then choose About This Mac. If you have macOS High Sierra, you are probably vulnerable. If you have anything else, stop here.
Second, you can protect yourself by making sure nobody other than you can get to your computer. So far, though theoretically possible, the vulnerability has not been exploited remotely unless you have enabled “Share my Screen.” If you feel confident that no bad actors will have access to your computer, you can stop here.
Third, reset the root password. Apple provides the 8 necessary steps at support.apple.com/en-us/HT204012 , Scroll down to the section entitled: Change the Root Password. In their step 7, if the option Edit > Change Root Password is grayed out on your Mac, then instead click the option Edit > Enable Root User and continue with step 8.
Please forward this to everyone you care about that has a Mac.