Why is it safer to have a personal security device to access online services?

Having a personal security device in addition to a password better secures you and your sensitive information.  The concept is like your ATM card: you have a personal, portable security device that can act as a digital key to identify you online.  You cannot get cash at an ATM without your card, something you have, and your PIN code, something you know.  The digital security devices work in a similar way.  You cannot access your desktop, laptop or company network unless you present a personal security device, typically a smart card or USB token with a smart card chip inside.  You also have to prove your identity by entering a simple PIN code.  Security pros call this two-factor authentication.