Ars Technica reports on a vulnerability where unencrypted Network Time Protocol (NTP) traffic can be exploited by man-in-the-middle attacks to arbitrarily set the times of computers to cause general chaos and/or carry out other attacks, such as exploiting expired HTTPS certificates.
While NTP clients have features to prevent drastic time changes, such as setting the date to ten years in the past, the paper on the attacks presents various methods for bypassing these protections.
There is a pdf of the report available.
(Score: 2, Interesting) by xav on Friday October 23 2015, @01:06PM
I'm under the impression you didn't understand chrysosphinx's answer, pardon me if I'm wrong.
With a local MitM attack, all responses from all NTP servers can be manipulated, and they will all appear to be in agreement.