[yuhong]

In the MDB format used in Access 2003 and older. BTW the user-level security and what was called "encryption" that was also supported in MDB format is no better. This encryption (which was based on 32-bit RC4) was so weak it was renamed "encoding" in Access 2003. All of these was ditched with the Access 2007 ACCDB format and replaced with real encryption based on CryptoAPI RC4 encryption (as termed is MS-OFFCRYPTO) introduced in Office XP (they did not adopt the new encryption introduced in Office 2007 file formats until Access 2010).

[ryandrake]

Any encryption method we come up with today can be considered "encoding" in the future, given enough time.

[acchow]

Except possibly AES.

http://security.stackexchange.com/a/25392