Riot Games has revealed in a mass email sent to League of Legends players that the North American account database has been compromised by hackers. Usernames, email addresses, "salted password hashes," and real names were accessed.
In addition, hashed and salted credit card numbers from around 120,000 transactions made in 2011 were also compromised. Riot reassured that the payment system used at the time has been defunct since July 2011, but it might be a good idea to change passwords anyway.
Emails only went to players with compromised accounts.