An organization's staff is distributed across varying locations, each with varying levels of network security. To strengthen their security posture for collaborative efforts, which measure would be most effective in ensuring authorized access to shared company resources?
Mandate email encryption for all internal and external communication.
Enforce a policy requiring users to change their passwords monthly.
Limit the connection times to shared resources to specific hours of the working day.
Implement multi-factor authentication for all users when accessing shared company resources.