How secure is Make Private in Memory Zone?

Can anyone advise; how secure is ‘Make Private’  in Memory Zone. 

For example, if I send a file to Box from my mobile having clicked Make Private and the file contains pin numbers, would this file be secure?

Yes, the files marked as private are encrypted so they are very secure. They cannot be opened if downloaded from the cloud unless you use the same owner’s Memory Zone app to make them “not private”.