Oracle Database Discussions

First let me say, that I am not hacking Oracle.

I am trying to get the opinion of knowledgeable DBAs that can tell me how to prevent or detect a hack.

I am writing a book and it involves a situation where a database is hacked to inject information into a record that was not there before. A DBA notices that the information wasn't there before. Assuming that whoever did that hacking changed whatever field and log needed to make it look like the data was in the database say two years ago, how would a DBA go about finding a record in some kind of audit log or other obscure database management system tool that would allow the DBA to detect when the data was actually committed.

there is a utility I came across that allows two or more databases to connect to one another and update information. How might you detect that the data came from an outside database? the idea being that the hacker was masking his trail by actually hacking a different database then using that database to update the other one.

Any other suggestion of a very sly surreptitious attack on a database that could inject data from the past into a database but still be caught through a very unknown method would be very helpful.

thanks a head of time