The Maunder minimum is known as the unique period of near zero sunspot activity during 70 years (1645–1715) which characterized by strong asymmetry in the hemispheres. In our work, we consider in details the nominal number of sunspot groups for each individual observer from the Hoyt and Schatten database since 1610. Sunspot activity is found to be underestimated because the database contains a lot of artificial zero values. Sources of these zeros come from short notices about absence of large sunspots, or archives which are not dedicated to the sunspot observations. We conclude that the Maunder minimum is a period of secular suppression of the 11-year cycle and non-stopped sunspot activity.