Is it relatively easy to hack Network Time Protocol(NTP)?

Question

I read somewhere that NTP is based on UDP and there's no security built with NTP communication so it is easy to spoof NTP responses. Is it true? Wouldn't that be a major security issue since most of the servers out there depend on NTP to sync their clock?

Answer 1

here is an interesting article that talks about some of the security concerns, it might be a bit dated, but a good read.