860K accounts from Stratfor (stratfor.com) were exposed in this breach. Besides email addresses, it included credit cards and passwords, which makes it a high-risk breach.
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Credit cardsEmail addressesNamesPasswordsPhone numbersPhysical addressesUsernames
In December 2011, "Anonymous" attacked the global intelligence company known as "Stratfor" and consequently disclosed a veritable treasure trove of data including hundreds of gigabytes of email and tens of thousands of credit card details which were promptly used by the attackers to make charitable donations (among other uses). The breach also included 860,000 user accounts complete with email address, time zone, some internal system data and MD5 hashed passwords with no salt.
Source: Have I Been Pwned (CC BY 4.0)