Security is that your Enterprise bean is secure inside the container and it cannot be accessed directly by any program or it cannot be altered by any program.
Concurrency is multiple access to ur bean ie., you need not have to write multithreaded program. The container will take care of it.
Persitence: The container will store and retrieve the data in a d/b. You need not have to take care of it.(in case of container managed persistence)
Hope i have made it clear
Anybody, Pls feel free to correct me if i am worong.
[This message has been edited by Kumar Vinay (edited January 02, 2001).]