http://suninatas.com/Part_one/web02/web02.asp 소스보면

        function chk_form(){
                var id = document.web02.id.value ;
                var pw = document.web02.pw.value ;
                if ( id == pw )
                {
                        alert("You can't join! Try again");
                        document.web02.id.focus();
                        document.web02.id.value = "";
                        document.web02.pw.value = "";
                }
                else
                {
                        document.web02.submit();
                }
        }

밑에 이런 스크립트 있고 주석으로 <!-- Hint : Join / id = pw --> 라고 쓰여있잖아

자바스크립트로 된 필터링을 뚫고 id와 pw에 같은 값을 넣어서 join하라고