note 25490 added to function.setcookie

What is the best and secure way to use cookie? Becuase I have used it to save the username, then I check the cookie, if the username has value "webmaster" (for example) then I give it full controll!! This is not secure at all!! because any body can add to the URL "?username=webmaster" and loging as webmaster? What Can I Do? I need help please. -- http://www.php.net/manual/en/function.setcookie.php http://master.php.net/manage/user-notes.php?action=edit+25490 http://master.php.net/manage/user-notes.php?action=delete+25490 http://master.php.net/manage/user-notes.php?action=reject+25490