Open NTP

Computers and network devices have a perversely strong need to have good agreement about what constitutes the current time (accurate precision time is critical for authentication related purposes, accurate event logging, and a host of other things). Most computers stay synchronized using Network Time Protocol (NTP). Oversimplifying greatly, NTP sets the local time by checking the time as reported by multiple trusted high-precision network-accessible clocks.

Impact of open NTP devices

Open NTP are amongst the most effectively mis-used DDOS amplifiers. Just like DNS, NTP is a UDP-based service, and shares the same weaknesses that DNS does (particularly problems with spoofed traffic, traffic amplification, and unnecessarily promiscuous access to servers). It is thus hardly surprising that NTP is being abused for DDoS attacks...