Apple has just published a security update which you can get from the OS X App Store > Updates:

This update addresses a critical security issue with the software that provides the Network Time Protocol service on OS X, and is recommended for all users.

Wayne Billing

Classroom Technology Support

Audio Visual and Classroom Technology Support

Computer and Network Support

130 Machray Hall Building

204-474-6649

204-807-3153 (cell)

204-474-7625 (fax)

Wayne_Billing@umanitoba.ca