Most likely you previously had ID theft and the IRS has been issuing you an IP PIN that is a unique 6-digit number. It should have been mailed to you or you can try www.irs.gov/ippinfaqs to obtain your PIN. If you have that IP PIN already, in Turbo tax you go to Personal tab, then Other tax situations tab, then drop down to Other return info and Start Identity protection PIN tab. And from my experience (not from TT support) you still have to enter a self-pin at the signature page.
