Symantec/Norton describes the Redirect 9 message this way at their Enterprise site: "This signature detects malicious advertisements leading to malware or exploits. Website hosts malicious advertisements which when clicked upon drops malicious files and compromises the security of the machine."

That leads me to suspect that you may have an Opera session, speed dial, or cache file that links to a problematic website which carries malicious ads. Such files, being part of your personal files, would normally survive a simple Opera uninstall/reinstall cycle and would have to be cleared out manually.