In 2013, the July cumulative update for Lync Server 2013 added two-factor authentication for the Lync 2013 client. As we mentioned in the introduction, the feature is available for Lync Online users, while on-premises deployment requires you to add a third-party solution. Two-factor authentication is based on the "something you know, something you have" principle, meaning that knowing a user's password without having an additional security item (a smart card) will not give access to Lync. An additional method could be based on "something you have" (a trusted device). We will see how to configure Office 365 (Lync Online) support for Multi-Factor Authentication (MFA). Office 365 MFA is a scaled-down version of Azure Multi-Factor Authentication service available to support both Azure and on-premises deployments. We will talk about it in the There's more… section.