Barack Obama has never been a Muslim, and is a committed Christian. There are numerous examples of people debunking this untruth.
Some people have accepted that he is currently a Christian but have wondered if he used to be a Muslim. Though there have been some interesting theories that ex-Muslims risk execution, the truth is that he was raised as a Christian and practices Christianity today.
If he is a Muslim, he is a very poor example of one. He does not engage in Salah (the prayer that Muslims must do five times a day) and he professes Christianity (which is a direct contradiction that Allah is the one and only God). As to the question of whether Obama is a secret Muslim: get a life.