Google has pushed an update to Chromecast bringing in some security enhancements. Here is the blogpost:

The Chromecast device has been updated to build 13300. This update will be rolled out over the next week, and you should receive the update automatically. The update is largely a maintenance release, and contains the following changes:

• Kernel update
• Security fixes
• Robustness improvements
• Security enhancements

Your Chromecast device will automatically download and install the update. Stay calm and keep casting!