If you own a computer running one of the three newest version of OS X, listen up. Apple recently issued an NTP Security Update for the latest OS X 10.10 Yosemite release, in addition to older builds for Mavericks and Mountain Lion that patches a major security issue.
By default, Apple says it does not “disclose, discuss, or confirm security issues until a full investigation has occurred and any necessary patches or releases are available,” so considering this is out there now, you should definitely apply the update.
Apple said that the OS X NTP Security Update fixes a part of the operating systems that allowed a “remote attacker… to executive arbitrary code” and said that “several issues existed in NTPD that would have allowed an attacker to trigger buffer overflows. These issues were addressed through improved error checking.” Specifically, it patches the bug in OS X Mountain Lion v10.8.5, OS X Mavericks v10.9.5 and OS X Yosemite v10.10.1.
Your computer may have already noticed the update and you may have been prompted to install it. If not, be sure to check now and get everything taken care of.