NTP server misuse and abuse
Misuse of a Network Time Protocol (NTP) server ranges from flooding it with traffic (effectively a DDoS attack) or violating the server's access policy or the NTP rules of engagement. One incident was branded NTP vandalism in an open letter from Poul-Henning Kamp to the router manufacturer D-Link in 2006.
Source: Wikipedia — NTP server misuse and abuse (CC BY-SA 4.0)