530K accounts from Unreal Engine (unrealengine.com) were exposed in this breach. Besides email addresses, it included passwords, which makes it a high-risk breach.
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Email addressesPasswordsUsernames
In August 2016, the Unreal Engine Forum suffered a data breach, allegedly due to a SQL injection vulnerability in vBulletin. The attack resulted in the exposure of 530k accounts including usernames, email addresses and salted MD5 hashes of passwords.
Source: Have I Been Pwned (CC BY 4.0)