Also accessed were hashed and salted credit card numbers from around 120,000 transactions made in 2011. Riot noted that the payment system in question has not been used since July of 2011 and that it is "taking appropriate action to notify and safeguard affected players."
If your information was affected, you will receive an email from Riot. All North American players will be required to change their passwords "to stronger ones that are much harder to guess." In the meantime, keep an eye on your accounts for any suspicious activity.