At 1:18 PM EST, Blizzard announced that the distributed denial of service (DDoS) attack affecting Battle.net has ended. Blizzard first acknowledged the attack on Twitter at 10:24 AM EST and even warned players of the attack in-game according to Kotaku, but going off posts to the Diablo subreddit, the game was experiencing significant problems as early as last night.
[#Bnet] The DDOS attacks that we were monitoring have ended. If you are still unable to log in try https://t.co/NY39q2slWoJune 25, 2023
Late yesterday, posts began cropping up on the Diablo subreddit questioning the game's server status. Posts from users Humdot, Angry-Gargoyle, and feiergiant all complained of what looked like unannounced server downtime, while MustaKotka noted that Diablo 2 Resurrected was also suffering connection issues. Overwatch 2 was similarly affected according to this post from MageWithoutMP on the Overwatch subreddit.
It is unclear who was behind the attack, and why it stopped when it did. Blizzard's announcement that "The DDoS attacks that we were monitoring have ended" makes it sound like the attackers ceased of their own volition. A DDoS attack uses a network of infected devices to overwhelm a server, and can be weaponized against targets ranging from individual users to massive online services. The attack's timing on the weekend seems like it was intended to affect the maximum number of Battle.net users.
Diablo 4's live service, always-online nature meant that players had little recourse but to wait the attack out—Diablo 4 has no offline mode, and even outside connection issues and DDoS attacks, this has resulted in a markedly different experience to the original games.