<P> Some special numbers are never allocated: </P> <Ul> <Li> Numbers with all zeros in any digit group (000 - ##- ####, ###- 00 - ####, ###- ##- 0000). </Li> <Li> Numbers with 666 or 900--999 (Individual Taxpayer Identification Number) in the first digit group . </Li> </Ul> <Li> Numbers with all zeros in any digit group (000 - ##- ####, ###- 00 - ####, ###- ##- 0000). </Li> <Li> Numbers with 666 or 900--999 (Individual Taxpayer Identification Number) in the first digit group . </Li>

When did social security numbers become mandatory at birth