The most effective way to detect an intrusion attempt is to periodically review log files, which record the activities and events on a system or network. Log files can provide evidence of unauthorized access attempts, malicious activities, or system errors. Configuring the router as a firewall, using smart cards with one-time passwords, and installing biometrics-basedauthentication are preventive controls that can reduce the likelihood of an intrusion, but they do not detect it. References: ISACA CISA Review Manual 27th Edition, page 301