Twitter has announced a two-factor authentication system it says will protect users' accounts from being hacked even if someone has obtained their password. Under the system, Twitters users will need both their password and a verification code sent to them as a text message on their mobile phone, SlashGear reported Wednesday. Users will need to enable the feature by going into their Account Settings, where they will check "Require a verification code when I sign in," click on "add a phone" and then provide their cellphone number. Users will then be sent a six-digit code in a text message they'll need to sign into their account, along with their password -- preventing unauthorized access to the account even by someone who has managed to obtain the password, Twitter said. A number of online services have offered similar two-factor authentication, including Facebook, Google, Yahoo and Dropbox.