Experiment, called TwiGUARD, lets Twitter users check if a follower is a spammer or if a link embedded in a tweet is malicious. TwiGuard also tracks the Twitter threat level, which will be adjusted according to active attacks on the service, providing attack details and how users can protect themselves. The site, which is still under development, uses a reputation-based algorithm to see if a user is a spammer or a link is infected. It also tracks Twitter threat levels, such as a jump in malicious activity or an indication of a larger attack.
Source: https://threatpost.com/twitter-security-experiment-goes-live-091009/72231/