Need help with security

[Brain In Vat]

I am writing the php code for a website. I had some difficulty with MySQL so the information gets written to txt files instead of a MySQL database. The problem is that if someone types in the correct url they can see a users information. I have been trying to set the permissions so that people cannot access the txt files, but the server can. Unfortunately when I set the permissions so that people can't access the database the program spits out a whole bunch of messages saying permission denied. I apologize for the lack of specifics, but I am not sure what information is safe to disclose.