Originally Posted by
DCAorBust
Probably the worst thing that could happen is closure and forfeiture of your dividend miles account. I haven't heard anyone speak from experience on this specifically, so it seems like low risk. OTOH, there have been a few reports of account closure for mileage accrual behavior that US didn't like.
Actually, if you do some searching here on Flyertalk, you'll find several people who have been caught. Some have been sued by the airline for the difference in fare. Now mind you, these are mostly people who did it many times for well over a year.
This of course in addition to having their frequent flyer accounts closed and miles forfeited.