Microsoft recently released a Convenience Update for Windows 7 and Windows 2008 R2 which will casuse majot inconvenience if using VMXNet 3.
The announcement at https://support.microsoft.com/en-us/kb/3125574 clearly says:
Known issue in this convenience rollup
Known issue 1
A new Ethernet vNIC may be created with default settings in place of the previously existing vNIC, causing network issues. Any custom settings on the previous vNIC are still persisted in the registry but unused.
To resolve this issue, uninstall the convenience rollup.
Microsoft is investigating this issue to determine proper course of action with VMWare. To resolve this issue uninstall the convenience rollup. Further information will be posted here as the investigation continues.
Be warned.. and always always follow change management and test systems before updating production systems.