Following denial of service attacks attributed to hacker group LulzSec, CCP restored EVE Online's Tranquility server and then took it offline again to protect its customers and investigate the situation. The server is currently back up, but CCP is prepared to take it offline again if warranted.
When Tranquility was first restored about an hour ago, Chief Operating Officer Jón Hörðdal wrote a letter to the community explaining why Tranquility was taken offline in response to the attacks. "It is always our approach to err on the side of caution in order to ensure the best possible service for our players and the security of their personal, billing and account information," he said, confirming that players' personal information and credit cards are safe.
Shortly following the restoration of Tranquility, CCP took the server offline again once the team "became aware of ongoing traffic flooding." As mentioned, the game is back up and is being closely monitored.
LulzSec took credit for the EVE Online attack on its Twitter page, along with similar attacks that occurred today against League of Legends, Minecraft and The Escapist magazine.