Twitter said Wednesday it was stepping up security measures for the popular messaging service following a series of high-profile breaches by hackers hitting media organizations and others. Twitter said it would implement a new login verification system, "a form of two-factor authentication" which is "a second check to make sure it's really you" when a user signs in.

Twitter said Wednesday it was stepping up its security measures for the popular messaging service following a series of high-profile breaches by hackers hitting media organizations and others. Twitter said it would implement a new login verification system, which is "a form of two-factor authentication" which is "a second check to make sure it's really you."

A Nazi-hunting group urged Twitter and other social media Wednesday to step up efforts to remove online "hate speech," citing a surge in incitement to attacks like the recent Boston bombings. The Simon Wiesenthal Center said Twitter has spawned nearly 20,000 hashtags and handles this year that are linked to terrorism and extremism, up 30 percent in the past year. "If we want to make it tougher for the terrorists to recruit, we need (actions by) Facebook, Google, Twitter and YouTube," the center's associate dean Abraham Cooper said at a Capitol Hill briefing.

By Gerry Shih SAN FRANCISCO (Reuters) - Does Twitter have a credibility problem? For many, a single fake tweet from the Associated Press account that briefly roiled financial markets on Tuesday, driving the Dow Jones industrial average down about 145 points, vividly reaffirmed the fearsome, near-instantaneous power of the 140-character message.