On checking the Windows Update site, the installation log shows that KB2446704 has been installed (green tick). However, on asking the site which updates are still missing from my PC, I am again offered the same file.
I've followed the MS troubleshooting advice re running the Windows Malicious Software Removal Tool (clean) and have run MalwareBytes and Emsisoft Antimalware with both being clear.
I downloaded the update and tried to install it in safe mode whilst logged in as Admin (again, as advised by MS), getting the error, "Windows installer service could not be accessed. This could occur if Windows is running in safe mode or if Windows Installer is not correctly installed."
This happens when some of te .net framework files have become corrupted. The procedure to repair windows update is quite tedious and described here
If you google your problem you will find several references but the advice given is as described in the above document