What are the extra security features which should be incorporated for an internet base database system?

A few things, you should password protect it and make sure it is not in your wwwroot folder.

What Corey says is correct. Ideally, the database should be in a folder with a non-standard name (i.e. not "database") because it's quite easy to download a DB when you know where it's stored, especially Access or similar DBs. Don't make the DB read-only unless you don't want online updates to data. Do add a password, but don't use it inside the script of each page - use it to establish the session for each user only. And be aware that Access DBs can only handle about 10-20 concurrent users.

TONY