Spam in the chat on minecraft server, how do i turn it off

so me and my friend just bought a server and each time we try to do anything do our chats get filled with everything that's happening, it's really bothering us so we would appreciate it if you told us how to turn this off

a picture: http://tinypic.com/view.php?pic=14uhqwp&s=8#.ViaUNH7hAok