Thi article explains the importance of using an authenticated timing reference when using a NTP time server (Network Time Protocol)
NTP
(Network Time Protocol) synchronises networks to a single time source using
timestamps to represent the current time of the day, this is essential for time
sensitive transactions and many system applications such as email.
NTP is
therefore vulnerable to security threats, whether from a malicious hacker who
wants to alter the timestamp to commit fraud or a DDoS attack (Distributed
Denial of Service - normally caused by malicious malware that floods a server
with traffic) that blocks server access.