"One in your mind - one in your hands" - this is how 2FA works. A simple password security is not enough for checking corporate mail in an internet cafe somewhere in the world or access private data via notebook and VPN. Only with an additional PIN-TAN access method or smart cards the necessary additional security is available.
The easiest method for 2FA is "PIN-TAN". In addition to a fixed password (PIN) a transaction number (TAN) has to be provided which is generated for each login. The TAN can be received via SMS, can be generated with a smartphone app or with a credit card shaped device.
Smart cards like the Yubikey do not show a TAN on a display but are sending this information directly from a non-compromisable chip to the requesting program like Windows logon, a VPN program or the hard disk encryption software.
SerNet supports DATEV user in all fields. "DATEV mIDentity compact" is an USB storage stick with integrated smart card reader. Only after authentication via smart card users are enabled to access DATEV's data center.