Which CUCM default global conference setting should be changed to ensure fraud prevention?

Advanced Ad Hoc Conference Enabled controls whether users can expand an ad hoc conference by adding more parties, but does not address the orphaned PSTN connection fraud scenario.

Block OffNet to OnNet Transfer prevents an external caller from being transferred back out to the PSTN, which is a separate fraud control unrelated to ad hoc conference behavior.

MCU Conference Bridge Custom Layout Index is a cosmetic display configuration for MCU video conferences and has no security or fraud prevention relevance.

By default, CUCM leaves an ad hoc conference active even after the initiating party hangs up, which allows a bad actor to bridge an expensive offnet PSTN number into a conference, disconnect, and leave the two parties connected at the organization's cost - a classic toll fraud scenario. Enabling 'Drop Ad Hoc Conference' ensures the conference is terminated when the controller disconnects, eliminating this fraud vector. Changing this from its default disabled state is a well-documented CUCM security hardening requirement.

Enable Click-to-Conference for Third-Party Applications governs external application integration for conference initiation and does not relate to the ad hoc conference toll fraud scenario.