Apple today released a new security update that’s designed to address a "critical security issue" with the Network Time Protocol service on OS X



From MacRumors:

The update appears to address a problem that was highlighted by the U.S. Government on Friday, December 19 and originally discovered by the Google Security Team. The vulnerability has the potential to allow an attacker to execute arbitrary code using the privileges of the ntpd process.Google Security Team researchers Neel Mehta and Stephen Roettger have coordinated multiple vulnerabilities with CERT/CC concerning the Network Time Protocol (NTP). As NTP is widely used within operational Industrial Control Systems deployments, NCCIC/ICS-CERT is providing this information for US Critical Infrastructure asset owners and operators for awareness and to identify mitigations for affected devices. ICS-CERT may release updates as additional information becomes available.

  Apple Issues Network Time Protocol Security Fix for OS X Users