Memcached is a memory caching system used to speed up a dynamic database of the websites by caching the data in RAM. It is a middleware so it lacks access controls and it should not be exposed to the public Internet. According to Shodan reports there are around 88,000 open Memcaches servers in the world. Cloudflare says a carefully carfted technique allows an attacker with limited IP spoofing capacity (such as 1Gbps) to launch very large attacks (reaching 100s Gbps) amplifying the attackers bandwidth.”]
Source: https://gbhackers.com/hackers-abused-memcached-servers/