Source: Internal Revenue Service
The United States Internal Revenue Service [IRS] stops and flags suspicious or duplicate federal tax returns that falsely represent your identity, such as your name or social security number. If the IRS suspects tax ID theft, the agency will send a 5071C letter to your home address. If you receive this letter, verify your identity at idverify.irs.gov or call the toll-free number listed in the letter.
If you are a victim of state tax ID theft, contact your state's taxation department or comptroller's office about the next steps you need to take.