The goal of the thesis is to analyse the purpose and implementations of Virtual File Systems (VFS) in modern operating systems, with focus on security issues that emerge in modern computing, where the code executed in a shared environment is rarely created (or even known) by the user executing it. Student will evaluate the feasibility of the inter-process isolation on a filesystem level, considering existing implementations of this principle, then propose a VFS architecture that fully utilizes these ideas. This architecture will be demonstrated by creating a prototype implementation of a VFS server within the HelenOS operating system. The work will be complemented with the discussion of changes required in other parts of the system to fully utilize the architecture, as well as the discussions of the possibility to utilize the implemented design to guarantee security for other types of mutually untrusted entities (such as user accounts).