We've all had it, every year.  It's become fewer and fewer over time.  It could be identity theft in total or it could be tax return identity theft, or it could be someone mailed in a return and misprinted a SSN.  You will never know.  Go to the IRS website and learn about tax return identity theft.  You will be required to mail in the tax return.  I then advise the client to freeze their three credit report accounts, possibly get a credit monitoring service like LifeLock or similar and apply to the IRS for an IP PIN.