> Does exist a procedure that auto-execute when an user try to connect
> to a database (like the AutoExec macro in Access)?

No.

> It would be useful to deny unauthorized access to the database in case
> of replacement of security.fdb.
> Thank you in advance for your response.

With regards,

Martijn Tonies
Database Workbench - developer tool for InterBase, Firebird, MySQL & MS SQL
Server.
Upscene Productions
http://www.upscene.com