An administrator is asked to implement toll fraud prevention in Cisco UCM, specifically to restrict...

To restrict off-net to off-net call transfers, an administrator can set the "Block Offnet to Offnet Transfer" service parameter to "On". This will prevent users from transferring calls from one external number to another external number.

The other options are not correct because:

A. Enforce ad-hoc conference restrictions: This will prevent users from creating ad-hoc conferences, but it will not prevent them from transferring calls.

C. Implement time-of-day routing: This will allow calls to be routed to different destinations based on the time of day, but it will not prevent users from transferring calls.

D. Use the correct route filters: This will allow calls to be filtered based on the destination, but it will not prevent users from transferring calls.