Periodically reviewing log files is the most effective way to detect intrusion attempts from outside the organization, as they can provide evidence of unauthorized access attempts, source IP addresses, timestamps and other relevant information. Using smart cards with one-time passwords or installing biometrics-based authentication can prevent unauthorized access, but not detect it. Configuring the router as a firewall can block unwanted traffic, but not log it. References: ISACA, CISA Review Manual, 27th Edition, 2018, page 361