Open unemployment is the unemployment which is visible and seen that some people are still want work. One such example is educated unemployment.
Disguised unemployment is the situation when some people are underemployed. They only divide the labour effort without any effective contribution to the growth of the sector. They are mostly found in Primary sectors because of unavailability of work for them. If they will be drawn out from work, there will be no such effect on production.
Disguised unemployment is more harmful than open unemployment because it often cannot be properly addressed due to its hidden nature and the potential of the human resource cannot be tapped.