Help Net Security had an interview with Christen Krogh, Opera Software's VP of Engineering:
In your opinion, what are Opera's strengths when it comes to security?
Our strength is that we take it really really serious. We have an excellent Q&A team that tests the browser versions prior to release, both manually, and automatically. We even have a group of skilled experts who call themselves "Evil Knights" working at finding holes and issues prior to launch.
Second, we try to develop our product in such a way that it helps the end users to browse safely. Our advanced Fraud Protection is one example of such a feature. Thirdly, whenever something comes up as a security issue after we have launched a product it takes first priority. We aim to never let a security issue stay unpatched.