It is “Freeze your credit report”, this got nothing to do with the SS admin, but a request from you to the credit reporting agencies (TRW,Experian, Equifax). There is a cost to do this but it’s free in California if you were a victim of any identity theft. I did it 4 years ago, and personally would not recommend it as it a pain in the A@# to unfreezes your credit reports (with 3 agencies by providing the PIN number) just to get approve for a car loan.
some link http://www.consumersunion.org/campaigns/learn_more/003484indiv.html#CA

Let me know if you want to do it, I have the letter request templates and addresses etc etc.