HLTV
In June 2016, the "home of competitive Counter Strike" website HLTV was hacked and 611k accounts were exposed. The attack led to the exposure of names, usernames, email addresses and bcrypt hashes of passwords.
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.