Keep an eye out for an email from Twitter asking you to change your password. It sounds like a bunch of passwords were reset as a result of some kind of hack that Twitter hasn't yet been able to identify.
The Twitter email reads: "Twitter believes that your account may have been compromised by a website or service not associated with Twitter. We've reset your password to prevent others from accessing your account."
If you received this message, it would be best to follow the steps provided in the email as soon as possible. Check your junkmail folder just in case you missed it.