Note: While privacy rules set on a Box File will work for preventing the upload from appearing in searches, the privacy rule will not prevent a user from accessing the file link if they were to obtain it.
For example, if there is a repeating group of Box File links on a page and a privacy rule for when "Current user is logged in", a logged out user would not be able to see that list of links. However, a logged out user would be able to access a protected link if it was shared with them somehow.