However, others believe that the last four digits when paired with birthplace or date of birth, could easily be guessed. Then Google can use the information to sell advertisements, according to New York Magazine.
Google found the conspiracy theory completely false. Although it change its policy asking for the last four digits, it said that it will discard all collected information.
To help us keep entries distinct and remove duplicate entries from any particular student, we asked parents for limited information, including the last 4 digits of a student's social security number. We later updated our forms when we recognized that we could sufficiently separate legitimate contest entries while requesting less information. . . . The city of birth helps us identify whether contestants are eligible for the contest, as winners must be either U.S. citizens or permanent legal residents of the U.S. The information isn't used for any other purpose.
Despite the various conspiracy theories out there, I don't think there was anything nefarious about what Google did. My phone and cable company routinely ask for the last four digits of my social and it's obviously an easy way to keep people with the same or similar names separate from one another.