Comment Properly configured hosts not impacted (Score 5, Informative) 179
If you saw this problem, your NTP time sources were not properly configured and diverse.
Consider using the NTP pool and not relying on so few sources to properly sync your time. Read 5.3.3 and 5.3.4 from http://support.ntp.org/bin/view/Support/SelectingOffsiteNTPServers for help to correct your NTP setup.