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.