Twitter has changed the way its "block" feature worked. Previously, user accounts you blocked could no longer follow the account you blocked them with, wouldn't appear in its timeline, and couldn't see its posts. They could still be retweeted by accounts you didn't block, and the people behind the accounts could log out or view your profile page on the web, but for all intents and purposes, "block" worked pretty much the way any reasonable person would expect it to - it made things more difficult. With the change, however, blocked accounts can now still follow the account you blocked them from, retweet and favorite it, and otherwise interact with it - typically you just won't see it (again, unless an account you do follow re-broadcasts it). In other words, the new Twitter "block" is more of a "mute". The only way to protect your account and content now is to make it private.