Microsoft also has a Message Center for Windows releases. The problem affects most supported Windows systems and Microsoft is presently investigating the issue. In yet another notable post-update Tuesday surprise, applications using Visual Basic 6, Visual Basic for Applications and VBScript may stop working after installing KB4512506, which is one of Microsoft's August security updates. Symantec is working on updates to Symantec Endpoint Protection to remedy the situation, according to this Symantec article. They are advising against manual August update installs. Microsoft and Symantec have set a temporary block on the delivery of the August updates for those affected systems.

The Windows updates are blocked or deleted by the antivirus program during installation, which may then cause Windows to stop working or fail to start. Symantec has identified an issue that occurs when a device is running any Symantec or Norton antivirus program and installs updates for Windows that are signed with SHA-2 certificates only. It's one of the 'known issues' this month, Microsoft explained: August patches are getting blocked for some users of Windows 7 SP1 and Windows Server 2008 R2 SP1 that use those antivirus programs. Microsoft also described similar SHA-1 distrust troubles for users of Symantec and Norton antivirus programs with this month's patches. It was broken by researchers last year using brute-force attacks, for instance. SHA-1, a 20-year-plus security algorithm for hashing data, is deemed insecure by the computer industry. Microsoft also previously announced that it was planning to distrust the use of SHA-1 for Windows systems back in February. Microsoft documented the matter in the Knowledge Base article referenced above, which includes a timeline for when SHA-1 gets distrusted for various Windows OSes.

The switch to SHA-2 only for Windows 7 and Windows Server 2008 R2 users took effect on August 13 ('update Tuesday'), when Microsoft released its August security and quality updates for Windows systems.

Windows security update kb4474419