Every Yahoo account was hacked. The hack was already one of the worst in history. Yahoo previously said it affected 1 billion accounts. The actual number is 3 billion. The attack occurred in August 2013. The attackers made off with all sorts of user data like phone numbers, birth dates, and security questions. Yahoo said passwords and credit card info weren't stolen. Yahoo is sending emails to affected users. With 3 billion users hacked, the 2013 data breach is the largest ever. Yahoo was also hacked in 2014. 500 million users were affected then making that the second largest ever data breach. If you're a Yahoo user, you should change your password. You should also change your security question. If you use that password anywhere else change that too. For better security, use a password manager like LastPass and enable 2-factor authentication. Being proactive can keep your data safe
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