Until technology is developed to monitor broker behavior accurately, today’s anti-mortgage fraud systems will not be able to detect every fraudulent brokered loan, according to a top industry executive. The batch of mortgages purchased by Freddie Mac through National City Corp.’s wholesale channel is a good example of tainted products that eluded both Freddie’s and National City’s automated sentries and later wreaked havoc in 49 Freddie PC mortgage pools.