I manually updated; however it seems to have corrupted my Avast program in some way, since it failed to open and run resident or the user panel, even after rebooting! I could not access the Alwil program files too. Panicking as a computer ignoramus does, I proceeded to uninstal Avast; the Windows add/remove progam option would not function so I used the Avast uninstal facility, which worked. However an Alwil folder entry remained in my Programs list, but I could not access it! So I am currently scanning my de-Avast-ed computer with Bitdefender Online scanner, a slow process. Any ideas Mr Avast rep?
I will probably try to reinstal Avast afresh afterwards, but I would prefer to reinstal the prior 4.7.817 if you could supply a link please (I'm guessing the web download would update to 4.7.826 by now).