A DDoS attack is an attack that makes the server unavailable for real traffic by sending it more traffic than it can handle through a botnet. You can read more about it at http://en.wikipedia.org/wiki/Denial-of-service_attack
Hello,
The attack we are currently dealing with is going to cause that. You may have been temporarily firewalled because of the heightened security settings or the attack may have knocked it offline again.
Hello,
The files it installed you can delete through the file manager. They are in the public_html folder. There is probably also a MySQL database which you can remove on the MySQL databases page in cPanel.
Hello,
The server is currently under a DDoS attack. For more information please see http://forums.x10hosting.com/service-alerts/108173-chopin.html#post617711