Отбить атаку на сервер

Сайты лежат. Получили письмо от хоста:

Dear Mr Evgeny Sokolov,

We have indications that your server has been attacked. Those responsible for this have been asked to solve the issue and to give us a statement on the cause of the attack.

This is an information email only and does not require any further action on your part.

In some cases such an attack can place a considerable strain on network resources and, as a result, a segment of our network can be adversely affected. In such a case the IP address of the attacked server can be blocked as a precautionary measure. You will receive a separate notification with further information if this happens.

Надо решить проблему. Срочно.