It has been a bad week for popular websites (getting hacked). Now Twitter has come forward and acknowledged that 250,000 accounts were hacked. The attacker may have had access to email addresses, encryption passwords and session tockens.
What is worrisome is that Twitter has claimed that the attack was "extremely sophisticated" and that they saw this same pattern of attach against other sites. Twitter is being proactive and is forcing users of those affected accounts to immediately change their passwords (those affected should have received an email from the company).
Stay vigilant. Use unique tough to guess passwords and change your passwords often.
Read the twitter blog entry here.