I could be completly wrong but on wikipedia it says
"Authenticated applications can use a (signed) permission request file to acquire permissions that go beyond the BD-J sandbox. Permissions can be acquired for:
* Reading and writing to local and system storage
* Using the network connection (to connect to defined servers)
* Access of the file system on the BD-ROM disc
* Title selection of other titles on the BD-ROM disc
* Control of other running BD-J applications"
"Security in BDJ is based on the Java platform security model. That is, signed applications in JARs can perform more tasks than a non-signed, such as Read/Write access to local storage, network access, selection of other titles on the BD-ROM disc, and control of other running BD-J applications."
im sorry if this has been mentioned but hopefully this helps