Opera software has released a new version of its Opera browser, version 11.01, for Mac OS X, Linux/UNIX, and Windows. The new version fixes several serious security issues, and incorporates a number of other improvements and bug fixes. The change logs have more details for Windows, Linux/UNIX, and Mac OSX. You can obtain the new version using the built-in update mechanism (Help > Check for Updates); Linux users should be able to get the updated package using the standard package management tools (e.g., Synaptic). Alternatively, you can download a complete installation package.
Because of its security content, I recommend that you update to the new version as soon as you conveniently can.