This property returns reference to list of all virtual
files defined globally. Virtual files are non-existent
files - but are visible to users that connect to your
server, and actually point to completely different location
on your file system.
VirtualFiles can be changed at run-time, and even when
users are connected.
When user connects to the server, this collection is
copied to User.VirtualFiles
collection - where you can change virtual files 'per
user' basis.