Server Got a Hacker/Attacker Help!

Hello everyone my friend is running his own serverand 2 weeks now everything working good(expept something he is working on like npc and etc) and yesterday we had an hacker/attacker on the server who used to chat in GM CHAT without beging a GM he used to reboot the server and making alllll the time day and night :/ that made my friend worried about the server and he closed it for a while till he founds a way to solve this problem... well anyone has any suggestion on what to do or how to resolve hackers/attackers?
thanks and waiting for an answer :)

Have you Fixxed the API Tool wen not then her are a tutorial:

[Only registered and activated users can see links. Click Here To Register...]

Yes, you should fixx API Tool coz, they use your server ports & server ip to get the admin access on your server.

You could change the ports too.

Search here in Board, you will find a lot of tutorials.

Best Regards