```ruby
class ApplicationController < ActionController::Base

  include ApplicationHelper
  protect_from_forgery with: :exception

  before_filter :authenticate!

  private
    def not_found
      raise ActionController::RoutingError.new('Not Found')
    end
end
```

Make the ApplicationHelper module methods private
user
```ruby
class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception

  before_filter :authenticate!

private
  include ApplicationHelper

  def not_found
    raise ActionController::RoutingError.new('Not Found')
  end
end
```
assistant