A company would like to develop a file share server on the corporate network. The file share would be used by employees and occasionally by customers, so parts of the file share would be accessible from the Internet. Some employees would share files with each other, but most would simply store files which would only be visible and usable by them. Some employees are in groups which would share files with each other, but those files should not be visible or usable by others.

What are your security recommendations for this file sharing system? 

Specifically, how would file security/sharing be implemented? What would be the network architecture for this system? 

What are the security risks for hosting this system on the corporate network?