Today there is a notification in my App Store’s MacBook Pro about OS X Mavericks 10.9.3 Update. I try to install it by click “Update” button in the App Store. You need to restart and install the update. It will take a moment for installing the update.
Please make certain that you’ve the latest version of OS X Mavericks. Kindly check using the App Store and make sure “No Updates Available” there. Beside that, click “About This Mac” to check the version of your OS X :).
If you’d like to follow the step by step, you’re able to read the instructions from Support Apple :
For detailed information about the security content of this update, see Apple security updates.