d553fd3e_soft_Access_Security_Apparatus__he_main_topic_of_this_article_
[Users, Groups, Permission] Database encryption
By default, Access mdb files are unencrypted... you can just drop them into a text editor such as Notepad, or better yet a hex editor, and read interesting data from them. (They could be edited in the same way, but skill would be needed to make edits that Access could later digest.) Access (and Jet) provide the option to encrypt the database, which prevents casual snooping of that sort. However, the encryption is not very strong, so it's readily crackable. The MSDN article "Exploring Microsoft Access Security" says "Jet uses a very weak method of encryption and should never be used to protect sensitive data." This is basically saying: Do not use the Microsoft Access product to store sensitive data, if bad guys have access to the mdb files. This is not completely damning -- many many useful scenarios can be implemented that don't feature bad guys, or that don't allow the bad guys access to the files.
The Microsoft Access Security Apparatus
"User-level security" or "Workgroup-file-based security": Governing who is permitted to view, add, edit and delete database objects (tables, queries etc), and to edit those permissions for other users. This is the main topic of this article.