What is the religion in Luxembourg?

Under Luxembourg law it is actually illegal to ask anyone what their religion is, however Luxembourg is overwhelmingly Roman Catholic.
Since 1979 it has been illegal for the government to collect statistics on religious beliefs or practices.[1] It is estimated by the CIA Factbook that 87% of Luxembourgers are Catholics, the remaining 13% being made up of Protestants, Eastern Orthodox Christians, Jews, Muslims and those of other or no religion.