1. A method of managing data security in a computer system configured to execute a plurality of applications, the method comprising: determining a security policy for a current application among the plurality of applications; determining an operating mode for the current application based on the security policy; if the operating mode is determined to be a secure mode, allowing the current application to access data stored in a specific region of a storage device and executing the application in the secure mode; and sharing the accessed data between the current application and another application among the plurality of applications when the another application is managed based on a corresponding security policy for the another application.