530K accounts from Battlefield Heroes (battlefieldheroes.com) were exposed in this breach. Besides email addresses, it included passwords, which makes it a high-risk breach.
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PasswordsUsernames
In June 2011 as part of a final breached data dump, the hacker collective "LulzSec" obtained and released over half a million usernames and passwords from the game Battlefield Heroes. The passwords were stored as MD5 hashes with no salt and many were easily converted back to their plain text versions.
Source: Have I Been Pwned (CC BY 4.0)