Today Apple released security updates for the two prior releases of macOS to address the high profile security problems that affect virtually every computer and smart device sold over the past two decades.
There was initially a question as to whether Apple would back-port these changes but it appears that they have. These patches mitigate the Spectre and Meltdown bugs as well as some others. I would highly recommend that everybody install these updates as soon as possible.
To update click the Apple logo menu in the top left corner of your Macintosh, Then click App Store and switch to the Updates tab.