It seems that Twitter dropping Bit.ly was true, as the site is now going to be launching a new URL shortener for use on the platform in order to combat the phishing problem that has exploded in Mentions and Direct Messages.

The company is launching "twt.tl", which will screen incoming links to the service being sent in a Direct Message (and thus email notifications), and check to see whether it's a reported phishing site, intercept and prevent the message from being sent.

Phising, as in the act of scammers obtaining a user's login data by pretending to be the destination site, is a massive problem for Twitter as it relies on third-party applications and a technology called "Basic Auth" where you need to input your Twitter credentials into other sites.

[Twitter Blog]