At this time, I am not aware of any security issues with Opera 7.11.
In the past, when a security issue was brought to Opera's attention, they had been very responsive and fast when issuing a new release fixing whatever the issue addressed. In the more than 2 1/2 years I've been using Opera, that one time was the only time I had been aware of a security issue requiring a new version of Opera to correct the problem.
Under Windows, I am using Sun's Java 2 Runtime Envorinment (JRE) version 1.4.2, and have not had trouble with it. Under Linux, I am not using Java. Opera for Linux requires an older version of a library than the one which came with the SuSE Linux distribution, in order to use plugins, therefore I cannot use plugins including Java. I don't believe I'm missing anything by not viewing Java applets under Linux.
UserAgent: Opera/7.11 (Linux 2.4.20-4GB i586; U) [en]