The problem is a serious one involving so-called Pegasus malware created by an outfit that goes by the name of NSO Group, which is known for selling spyware to governments, and that's exactly what this nasty does – allows an attacker to spy on your device.
That's why you should act quickly to make sure that these vulnerabilities are patched up on your Mac.
Patch it up
Apple has actually issued a pair of patches. The main one addresses the problem for the OS on both Yosemite and El Capitan – it's not mentioned if the flaw also affects preview versions of macOS Sierra.
The second update is for Safari, and cures a memory corruption issue present in the browser. This fix is actually included in the above patch, but is available separately for those who don't install that (as mentioned, it only pertains to Yosemite and El Capitan).
At any rate, head over to the App Store and click on the Update tab (top-right) to patch your system up appropriately.
It's a bit of a tired old record now, but yes, this is another small lesson in how Mac security isn't bulletproof and shouldn't be taken for granted. As we saw back in the spring, Apple computer users have also come under fire with ransomware this year, the current belle of the malware ball.
- Also check out our macOS Sierra rumor round-up
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Darren is a freelancer writing news and features for TechRadar (and occasionally T3) across a broad range of computing topics including CPUs, GPUs, various other hardware, VPNs, antivirus and more. He has written about tech for the best part of three decades, and writes books in his spare time (his debut novel - 'I Know What You Did Last Supper' - was published by Hachette UK in 2013).