&gt;Having knowledge of a Social Security number was assumed to be authentication<p>No the people that designed and implemented Social Security knew it was not secure for identification purposes,  the first few decades of the program even had &quot;Not to be used for Identification&quot; on the card.<p>Then the government, and financial industry got lazy and said &quot;well since the majority of people already have these numbers assigned to them lets just use them for Identification as well&quot; and made it a defacto National ID.  Something it was never designed for, nor secure enough to be,