Out of the following, which is the most effective way to protect against rogue modems and the risk they introduce?

War dialing is a detection technique used to discover active modem lines by scanning phone numbers, not a preventive control that stops rogue modems from being exploited.

Egress firewall filtering monitors and blocks unauthorized outbound traffic leaving the network, making it the most effective preventive control against rogue modems. Even if a rogue modem is physically present, egress filtering can detect and block the unauthorized outbound connections it attempts to establish, preventing data exfiltration and back-channel access. This is a proactive preventive measure rather than a reactive or detective one.

Dial-up modem connections use the public telephone network and bypass the corporate firewall entirely, making filtering modem lines at the firewall technically infeasible in standard architectures.

Disabling PPP is impractical to enforce across an enterprise and does not address the physical risk of unauthorized modem hardware being connected directly to workstations.