Several years ago some NW employees were arrested for fraud. They had a racket going where they would find travellers who were not already receiving FF credit who had a ticket that would earn enough miles to get a free ticket, they would sign them up for Worldperks unbeknowest to the traveller, and collect the miles and free ticket. I believe they were caught eventually when folks started trying to claim retroactive credit for trips and learned that credit had already been collected.