Anti-racism group SOS Racisme said it was illegal because French law did not allow the compilation of personal data without the individual's consent.

BBC: Apple drops 'Jew or not Jew' app in France

French laws enacted after World War II ban the compilation of information about religious affiliation without permission.

BBC: Apple drops 'Jew or not Jew' app in France

Because this procedure, called compilation, is hard to reverse, firms can sell a program without revealing the instructions that underlie it rather as Coca-Cola can market soft drinks without giving away its secret recipe.

ECONOMIST: Computer programming