Two months ago Microsoft released a security update designed to fix two flaws in the Windows kernel. Unfortunately, this update would cause a Blue Screen of Death on many users computers. After some research, it was discovered that a rootkit was the cause of the crashes and Microsoft stopped automatically serving this update.

Microsoft has since restarted distribution of this update only after it had found out a way to block the rootkit-infected computers from receiving the patches.
Jerry Bryant who is a general manager with the Microsoft Security Response Team said the following:

“If detection logic included in Automatic Update discovers abnormal conditions in certain operating system file configurations, the update will fail and customers will be presented with an error message that offers alternative support options,”

While this will prevent the Blue Screen of Death appearing, it will leave users vulnerable to the exploit the update was originally designed to patch. No exploits of this flaw appear to exist in the wild just yet, but Microsoft warns that exploit code is likely to be developed.