Microsoft has released an emergency patch for all versions of Windows to address a critical security vulnerability. They have provided details of the update here:
We highly recommend that all ResNet users on Windows (including those using Parallels, Fusion, or Bootcamp), run Windows Update immediately to obtain the patch.
Lenovo has released information regarding a security vulnerability found in certain laptop models. We highly recommend that all ResNet users that own a Lenovo product check the following list and, if they own one of the affected models, immediately follow the instructions to update their laptop firmware and remove the vulnerability.
Microsoft has released the Windows 10 Media Creation Tool, which allows you to upgrade your computer to their latest operating system earlier than waiting for the update through Windows Update.
If you’d like to get Windows 10 up and running on your computer ASAP, check out the following instructions from Microsoft: