Re: To the IRS... Here's a free clue!
I know about the e-file PIN, but as you say the problem is that it isn't persistent. It isn't foolproof, since your accountant could be hacked, but the main source of the data used for this scam is getting a list of names and SSNs. Sadly that's all you need to file under someone else's name.
I don't know the details of how the scam works exactly, but I would think if they filed under my name they wouldn't know how much income and withholding was on my W2. I guess the crooks are relying on the IRS helpfully 'correcting' a flawed return that doesn't include accurate info, but they need to start setting those aside for extra checking for fraud - or just plain kick them back and make the person refile.