Just this month, Microsoft released an update for the System Center 2012 Endpoint Protection and Forefront Endpoint Protection 2010 clients that apparently can have some severe consequences if users regularly download content from the Internet.
The problem has been observed on Windows 8.1 computers running Internet Explorer 11, but could affect other configurations, too.
Microsoft explains the cause this way…
On some systems, an earlier version of mpoav.dll is loaded, or remains registered, during the installation of the 126.96.36.199 client. This configuration can lead to a conflict in binaries, resulting in Internet Explorer 11, or other web browsers, blocking all downloads. Users will see the message “This file contained a virus and was deleted” when attempting to download any file.
Microsoft is currently working on a fix, however, for those that already installed the client update and experiencing the reported problem, uninstalling and reinstalling a known working version from the October 2014 release (version 4.6.305.0) will reenable download capability.
To keep the issue from affecting more customers, Microsoft is removing the broken client from its update servers today.