Answer Description
The important information here is that the information was shared on the network. All of these options are good for security, but only using least privilege on the network directory will affect this specific problem.
Wikipedia
In information security, computer science, and other fields, the principle of least privilege (PoLP, also known as the principle of minimal privilege or the principle of least authority) requires that in a particular abstraction layer of a computing environment, every module (such as a process, a user, or a program, depending on the subject) must be able to access only the information and resources that are necessary for its legitimate …
Principle of least privilege - Wikipedia, the free encyclopedia