Hi venkat,
You can apply security at various levels in businessobjects. below are some of them
Security at Object level - Using Case and Decode
Security at Universe level - Using Security profiles
Security at Folders level - In CMC as per content management plan
Securiry using external tables by using BOUSER variable
To understand more about Folder level security, have a look here.
http://blogs.hexaware.com/business-objects-boogle/business-objects-content-management-planning/
Regards
Mani