BT Turns Sheriff On Lawbreakers To Stop Fraud By Sheridan Nye, Total Telecom Telephone companies are reluctant to discuss figures, but fraud is believed to siphon between 3 percent and 6 percent of revenues -- billions of dollars -- every year as telephone hackers target unprotected switches. One of the most vulnerable areas is dial-through fraud where, for instance, a call to a voice-mail system can be redirected to another number. "Telcos are losing billions of dollars every year," said Cooper. "So even if they can stop a fraction of it, they are going to make significant savings."