When a software update is broken or is bugged, users will have to wait for a followup update that will hopefully address the issues. However it seems that in a recent Windows 7 update, the update proved to be broken to the point where it would actually prevent the installation of a newer update that could potentially fix it.
According to Microsoft, they have recently confirmed that the KB3004394 update issued on the 10th of December to Windows 7 users could cause several problems, one of which is the prevention of the installation of future and newer updates. This appears to be a Windows 7-only problem as Windows 8 users are said to be unaffected by this.
For those who let their computers update themselves automatically, there is a good chance you might have already installed the buggy patch, although thankfully Microsoft has since released a tool in which the patch can be removed. If you’d rather do it manually, you can go to your Control Panel > Programs > Programs and Features > View Installed Updates, and right-click on the KB3004394 update to uninstall it.
If you do not see the patch in the list, then chances are you haven’t installed it yet. It is unclear as to how big of a problem this could be for users, but if you have an AMD GPU, AMD’s Robert Hallock claims that it could potentially prevent the installation of GPU drivers, so if you’d rather not run into any issues later, you should probably go ahead and remove the update now.