It is always a good idea to have current security software running on your computer. It is also important to be diligent about updating your computer with security patches. In the event your computer is infected, or you use an infected computer, multi-factor authentication offers some measure of additional protection.
If someone tries to use your logon and password from another computer, they will need to know the answer to your challenge question. After a few incorrect attempts your account will be locked. Resetting an account that has been locked requires additional information that only you will be able to provide or receive via your e-mail account.