The Register writes Microsoft messed up with this week's Patch Tuesday rollout as systems with Windows Server 2008 R2 running VMware experienced disconnects. The issue was caused by lost static IP addresses.
The problem appears to afflict machines configured with static IP addresses.
During the installation of the update the NIC is replaced by another configured for DHCP, potentially knocking the machine off the network.
Administrators are reporting that rectifying the problem requires a little more effort than simply switching back from DHCP since the original NIC may still be present, just hidden.
Microsoft has remained tightlipped on the issue, leaving it to users to work out what part of the update borked their carefully crafted networks.