Authentication is the most effective control for the scenario because it directly addresses who is using the public computers:
* User Identification: Authentication requires users to identify themselves (e.g., library card, login credentials) before accessing the computers. This links actions to specific individuals, making it easier to control unauthorized activity.
* Policy Enforcement: Combined with other controls (e.g., content filtering), authentication enables the library to implement policies restricting downloads. If users violate the policy, their identities can be used for consequences.
* Deterrent: Knowing they can be identified discourages users from attempting illegal downloads.