It's a long-standing myth that Mac computers are immune to viruses. It is true they still aren't nearly as vulnerable as, say, Windows computers, but a number of nasty Mac viruses and security flaws have popped up over the years.
Now, there's a new security flaw Mac users need to know about. It has to do with the software that wakes a Mac up from its default sleep mode.
According to security researcher Pedro Vilaca, when the wake-up program runs, it opens a security hole that a hacker can use to remotely modify code and slip a rootkit on to the Mac. A rootkit is a very sneaky virus that's almost impossible to detect and remove.
Not every Mac is affected by this security flaw; Macs released after mid-2014 have the flaw fixed. If you have a Mac from before that, however, you're vulnerable.
Right now, Vilaca says this flaw requires a targeted attack, so hackers won't be able to compromise millions of Macs at once. Plus, there are easier ways for hackers to break into a Mac. So the threat to you is minimal.
If you want to be sure you stay safe, you can go into your Mac's power settings and tell it not to go to sleep. Just go to System Preferences, select Energy Saver and then adjust the sleep settings so it stays awake or shuts down entirely.
Of course, if you have a laptop and turn off sleep mode, that will cause it to drain the battery faster, and a desktop will use more electricity. Shutting down all the time is just annoying.
Another point about this flaw is that it will require a malicious program or site to run. If you avoid downloading and running programs from phishing emails, or clicking on suspicious links, you should greatly decrease your chances of having this happen.
It's unclear if Apple is going to release a fix for the affected Macs, or even if it can. The problem is in the computer's EFI (the new version of BIOS), which takes a little more work to update than a typical Mac software update.