The server went down suddenly in the morning of 18 June (UTC), with Hypixel said on their website that network suffered a large-scale direct denial of service (DDoS) attack. These DDoS attacks have continued over several days.
The team said their
top priority is to mitigate the impact of these attacks as quickly as possible while working on permanent solutions that will shield [them] better from future attacks.
The server had been suffering from connection issues for several days before their emergency downtime, with the team having
identified the issue with an upstream provider causing
intermittent connection issues to the server and forums.
Hypixel have identified the cause of the security issue as a recent configuration change in their server hosting having left the network vulnerable.
On 19 June Hypixel stated that they had moved all their server hardware to run under Cloudflare, making the server
100% Cloudflare, with full DDoS protection from now on. However, this required the moving of many physical hardware units to the new network, which they say
has taken a fair bit of time.
Today Hypixel is running an initial test with their new setup, with a
severely limited player count and regular downtime. In their update edit they state that
all of the new hardware has been configured to the new network and all the core servers and minigame servers are working great.
Only players with paid ranks are allowed on the server as Hypixel transitions to limited maintenance mode. Any time-sensitive purchases players have bought will have their durations extended.
Historically, Hypixel is no stranger to massive DDoS attacks. The team say they have
dealt with DDoS attacks for well over 8 years now and we have a great understanding of the [current] situation. Three years ago, in April 2018, Hypixel switched to using Cloudflare for DDoS protection after a series of attacks by Mirai botnets.