Demonetization programme required that people deposit all their cash holdings with banks. They did , so did many tax evaders also. In order to find tax evaders out of millions of depoists, CBDT started Operation Clean Money under which the tax administartion tried to get exaplanation regarding the cash deposits from tax payers through efiling website . The first phase exercise generated only 7.3 Lakhs responses which is merely 50% of the total nos of cash depositors ( about 15 Lakhs). So , the balance 50% is a large chunk of accounts who have not responded to SMS and email……..( I suspect many might not have facilities ,,,so may not be aware also) .