(Reuters) - Twitter Inc began introducing new technology on Wednesday to shore up security for users, responding to a spate of recent attacks on prominent accounts including those owned by the Associated Press and Financial Times. Twitter said in a blog post it has begun to introduce "login verification," a form of two-factor authentication in security industry parlance. The feature asks users to confirm their identity after a typical log-in, by sending a six-digit code to smartphones that must then be typed in to complete a sign-on. ...