Yandex Dump
In September 2014, news broke of a massive leak of accounts from Yandex, the Russian search engine giants who also provides email services.
A security/data breach is the intentional or unintentional security incident in which information was accessed without authorization. Release of secure or private/confidential information to public can hurt businesses and consumers in a many of ways.
Other reference: security compromise, data leak, information disclosure, information leakage, data spill.
List of all known breaches.
In 2014, a file allegedly containing data hacked from Coupon Mom was created and included 11 million email addresses and plain text passwords. On further investigation, the file was also found to contain data indicating it had been sourced from Armor Games.