The Data Masking transformation returns a Social Security Number that is not valid with the same format as the source. The first three digits of the SSN define the area code. The Data Masking transformation does not mask the area code. It masks the group number and serial number. The source SSN must contain a valid area code. The Data Masking transformation locates the area code on the High Group List and determines a range of unused numbers that it can apply as masked data. If the SSN is not valid, the Data Masking transformation does not mask the source data.