Thanks Gargamel360. Good to know there isn't a problem.
That's interesting because my Avast! scan started at 6pm and finished just after 7.30pm (it was a full system scan). According to the maintenance window the last update attempt was at 4.49pm... so quite a bit before the scan started.
I did look at my Windows Updates just now, and noted that it checked for Windows updates and updated the definitions for Windows Defender at 7.08pm, which might explain why the windows defender file was there. (Usually it checks for updates in the morning when I boot up, so I don't know why it did it then).
OK Pondus - I shall do that tomorrow. Thanks.