Microsoft's security fixes come out every month like clockwork with Update Tuesday. But Apple's updates and security patches are much more sporadic.
So when they are announced, you should pay attention. Apple is calling this a "critical security issue," so Apple users need to listen up.
Apple has issued a warning for "OS X users following the discovery of a vulnerability in the Network Time Protocol which affects the Yosemite, Mavericks and Mountain Lion operating systems."
The bug was actually discovered by a member of the Google Security Team earlier this month, but Apple didn't release a fix until now because the company says that it wants to be sure that the problem is real and complete a full investigation before alarming the public.