Hello I posted about this before but it never got addressed please look into this as I think it is an important security measure.
The front end upload widget allows users to add a new category and also to add files. In settings if the private files box is clicked (Access to files is only permitted to owner and administrators) it does restrict visibility of files from other users however it does not make categories they add private! I know it says that it will make files private and it does what it says it will do but if you are using this option as a confidentiality security requirement the categories need to be private otherwise it jeopardizes confidentiality.
Absolutely great plugin by the way.