"When someone attacks your company's I.T. systems, they're usually after one thing: your data. Pilfering information about employees, clients, intellectual property, or business strategy from well-guarded databases has typically been an inside job perpetrated by employees with a certain level of access to the database system. This is still the case, but databases are becoming more vulnerable to the outside world as Web-facing apps demand faster access to information and databases move closer to the network perimeter, opening them to network-based attacks."
This is a very good 4 page article discussing the current state of Oracles security. I particularly like the quote "Generally speaking, databases are very difficult to attack," MacPherson says. "They're the most secure aspects in a network." on page 4