Opera 10.01 is a recommended security and stability upgrade.
Certain domain names can allow execution of arbitrary code
Specially crafted domain names can cause a memory corruption in Opera, which may lead to a crash. Successful exploitation can lead to execution of arbitrary code.
Opera may allow scripts to access feeds
Opera may allow scripts to run on the feed subscription page, thereby gaining access to the feeds object. This can be used for automatic subscription of feeds, or reading other feeds.