Not a lawyer, and this topic generally starts a long thread full of silly myths and misinformation. However, any original work is legally copyrighted to the author when he creates it. It is not necessary to register it to have copyright, under US law at any rate, it is automatic. "Registering" this copyright just provides one accepted method of verification should you subsequently need to prove the creation date in court. There are many other less expensive/free methods of establishing authorship and the creation date.