Every Mac user should be backing up the files on their Mac. The easiest way to do this is to use Time Machine, which is part of macOS. You can get a cheap external hard drive and start doing this today. Time Machine is simple and automatic and can save you from disasters, as long as you start using it.
Many Mac news sites and blogs are reporting about a way that someone can gain access to your Mac without your password. However, the danger is usually overstated as someone needs physical access to your Mac to use the exploit. In this video I'll show you the problem and also a simple way to prevent it. However, Apple will probably have a fix for this in the next few days or even hours.
Over the last few weeks many people have been reporting unwanted Calendar invites, usually looking like junk email with a sales pitch and links. It is difficult to get rid of these invites without notifying the sender that you either declined or accepted it. But there is a method to quietly delete the invite. A better solution is to switch to email notifications of Calendar invites until Apple fixes the problem.