Antiviruses suddenly stopped working on all versions of Windows

Antivirus solutions from different vendors are showing malfunctions after the installation of Windows security patches released on April 9.
 
Antivirus solutions from Sophos, Avira, ArcaBit, Avast, and recently McAfee reported security issues after the installation of the fixes released by Microsoft.
 
Microsoft is aware of the problems reported by its users with their antivirus solutions and already included several antivirus software to the list of known issues.
 
Users of the affected machines are observing sudden system freezes and performance degradation.
 
In some cases, users of systems running Windows 7, 8.1, Server 2008 R2, Server 2012, and Server 2012 R2 reported that they were able to log in, but the process takes more than ten hours.
 
Experts observed that safe mode is not affected by the issues, experts suggest to run in safe mode to disable the antivirus and allow the machines to boot without problems.
 
“Sophos additionally reports that adding the antivirus software’s own directory to the list of excluded locations also serves as a fix, which is a little strange.” reported ArsTechnica.
 
“Avast recommends leaving systems at the login screen for about 15 minutes and then rebooting; the antivirus software should then update itself automatically in the background.”
 
Update for Sophos, Avira, and ArcaBit users, have been blocked by Microsoft. McAfee is investigating the issue, while ArcaBit and Avast already released updates that address the problem.
 
According to experts at Avast and McAfee, the root cause of the problem is the change that Microsoft made to CSRSS (“client/server runtime subsystem”) component that manages Win32 applications. The experts believe that antivirus solutions are blocked while attempting to access some resource.
 
At the time it was difficult to understand what has happened and if the problem could definitively be solved by applying antivirus updates of fixes of the operating system.

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