Many regions of the world today are considered hostile to Christianity and restrict all forms of missionary work. Thus the notion of "security" has become a well developed part of the missionary enterprise. For example, if believers are gathered together at all it is often in the form of an "underground" church. Spreading of the gospel is limited to "low-key witness" (i.e. that which does not arouse too much attention).
   The primary problem I see with "security" is that it does not adequately honor God. The way God interacts with His world is definitively public, not secretive. If actions speak louder than words, then secrecy does a terrible injustice to the message that the Good News is for everyone, that God is the God of all people, and that He is sovereign over all the affairs of the world.
   Second, secrecy is based on limited human reasoning, not the revelation of God. An entire generation of Hebrews was denied entry into the Promised Land because they listened to the report of giants in the land rather than God's command to enter that land. We have not been commanded to go in secret (Matthew 10:27, 2 Timothy 1:7-8).
   Secrecy is also based on a false theology of persecution. We from the West export our expectations of a safe and comfortable Christianity. In contrast Jesus said, "If they hated me they will hate you also" and Peter said, "Rejoice that you participate in the sufferings of Christ."
   Finally, secrecy does not do the job of getting the gospel out to an entire community. For good reason we see the Lord and His apostles at times engaging the public. Their message soon saturated the society and became a public issue.
   This has been a brief introduction to the topic of secrecy. A longer treatment of this topic can be found here.