Microsoft has released an emergency out-of-band patch for IE 8, 9, 10, and 11. This includes a special update for Windows XP in the interest of safety – even though this older O/S is no longer officially supported.
QUOTE: At approximately 10 a.m. PDT, we will release an out-of-band security update to address the issue affecting Internet Explorer (IE) that was first discussed in Security Advisory 2963983. This update is fully tested and ready for release for all affected versions of the browser. The majority of customers have automatic updates enabled and will not need to take any action because protections will be downloaded and installed automatically. If you’re unsure if you have automatic updates, or you haven’t enabled Automatic Update, now is the time. We have made the decision to issue a security update for Windows XP users. Windows XP is no longer supported by Microsoft, and we continue to encourage customers to migrate to a modern operating system, such as Windows 7 or 8.1. Additionally, customers are encouraged to upgrade to the latest version of Internet Explorer, IE 11.