LinkedIn is the latest web property to join the growing crowd of companies that have implemented a version of two-step authentication. Two-step--or two-factor--authentication make accounts more secure by requiring more than just a password. Users often have to have access to their cell phone to log in on an unrecognized account.
In LinkedIn's case, users will be required to input a code sent via SMS to log in on an unrecognized device. LinkedIn director Vicente Silveira notes, "Most Internet accounts that become compromised are illegitimately accessed from a new or unknown computer. When enabled, two-step verification makes it more difficult for unauthorized users to access your account, requiring them to have both your password and access to your mobile phone."
Twitter and Apple both recently added two-step verification. For Twitter, it might have been too little, too late as they had already suffered from a number of high-profile hackings, including one of the AP's account that led to a rapid drop in the Dow Jones from a fake tweet.