This has never happened to me with Marriott, but I've gotten similar messages from other websites in the past. It has always ended up being someone trying to scam my account, log in repeatedly with the wrong password, etc. that results in them locking the account until I call in and verify my identity. Could it be that simple in this case? You would think the "internet specialist" would be able to clear it up, but I agree with the others who say that the few facts we know don't seem to line up so far...