I installed the November 2018 Windows and Office updates for Windows 10.
A few hours later an automatic McAfee update arrived but its installation seemed unusually slow, creeping up to 10% installed, then no more. I left it alone and got on with something else and eventually the blue McAfee activity disc disappeared as though the update was installed.
Not long afterwards I noticed that the hard drive was running flat out all the time and Task Manager showed it at 96-100%, even when there was no obvious activity (the CPU and Memory were still normal).
I tried various solutions including restarting the computer, but the problem persisted.
I assumed it must be either the Windows update (KB4023057) or the McAfee update that was causing it.
I uninstalled KB4023057 and left it to settle down, but still the hard drive was up to 100%.
I then ran McAfee Virtual Technician.
It found one fault, which I already knew about, which was that Site Adviser service was turned off, but this was done intentionally several weeks earlier and had not caused any problems.
So I did not accept the offer to restart the service but closed Technician without making any changes (or so I thought).
But immediately after closing it the hard drive usage went down to normal (i.e. 0% except when there was activity).
I reinstalled KB4023057 and waited to see if the hard drive would stick at 100% again, but it did not.
I later checked for the latest McAfee update and this was installed normally.
So far there has been no recurrence of the problem.