My minecraft server got hacked, what do i do?

I guy came on and hacked the server frame and oped himself so i closed the server and banned his ip i don't know if that will work so i want to know what do i do

Added (1). my server is a bukkit server

If you use a server developer online then the website should have a whitelist option. You should create a whitelist and ONLY put on trusted player's usernames on the list. That way, anyone who is not on the list will not be able to join the server. If you really are concerned, try make the spawn area a giant lava pit. Then when he joins he will always fall in the lava.