The 10/40 Window is a term used by Christians for a selected section of the worldmap where general conditions are hard to live the Christian life. It is hard due to the environment (desert), other faiths and poverty. Plus it is hard to speak openly about their faith.
YWAM is certainly operating in the 10/40 window, but due to the risk of endangering the lives of believers and missionaries there is not much shared. In a way it is not a secret, but information should be handled with care. Prayer is always welcome for the people who live and work in this area.