With tools like the Twitter Password Decrypter or Twitter Hack it is possible to get into several twitter accounts (only use it for your own lost!) and to alter the user data including the login password!
With the password decrytper tool the person who lost his password has the ability to instantly hack (recover) the user details, in case a person cannot use the twitter password reset function with success. Since most web sites log alot of details for visited websites it is possible to extract and decrypt the login username and password. The tool checks every possible location the passes could be stored and immediatly starts to decrypt them to plain text. The data can then be used to log into the twitter account again.
After you got inside the account again, change your password to a known one do not change anything other...and don't forget it again!