NTP server misuse and abuse covers a number of practices which cause damage or degradation to a Network Time Protocol (NTP) server, ranging 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. This term has later been extended by others to retroactively include other incidents. There is, however, no evidence that any of these problems are deliberate vandalism. They are more usually caused by shortsighted or poorly chosen default configurations.