The taxpayer will receive a notification confirming the tax-related ID theft incident along with an assigned IP PIN for future tax-return filings. Once issued, IP PINs must be used when filing or e-filing tax returns with the IRS, including any late-filed returns for prior years being filed in the current filing season.
https://www.irs.gov/site-index-search?search=ip+pin&field_pup_historical_1=1&field_pup_historical=1
