A security token is coupled to a computer and is available for use by both local and remote processes for on-demand response to a challenge. To minimize the security risk of an unattended session, the challenge may be issued to verify the presence of the token. When the token has a user interface, it may be used in conjunction with the computer to require that a user also participate in transferring displayed data between the token and computer. This helps to ensure that not only the token, but the user are both present at the computer during operation. For the most sensitive operations, such a confirmation may be required with each data submission.