Riot Games posted a notice on their forums letting players know that the EU databases were breached by hackers. While they're sure that no payment information was compromised, it's unclear what personal information may have been stolen. At the very least they're encouraging players to change their passwords.

This sort of thing seems to be happening more and more often in the gaming world. Kudos to Riot though for the swift announcement and action on their part, we've already seen other companies try to downplay or cover up such problems. Once again, even if you're not in the EU, it may be a good idea to go change your League of Legends password.