Need Urgent Help

I have the same problem as some others.My Yahoo id has been hacked by someone.his yahoo id is vicky_y2k8.Everytime i open my message archive i get a message from the above id.”ur id hacked by Magic PS v1.5 SE++.Is there any way to stop it??..I have tried changinf my password many times including using special characters and all but still tht message appears in my archive with the new pass word.please if some one can help me.If u knw how to avoid this or protect my id against it please tell me the coreect procedure.