Avast just ran a Smart Scan without me asking for it. Can anyone tell me how to stop it doing this?
You have probably been caught out by the run this as a scheduled scan.
If you run a Smart Scan on completion the interface has an option to run this as a scheduled scan, this option is pre-checked. So if you don’t notice that, bam it runs as a scheduled scan. So you may have to run it again and ensure that you uncheck the schedule scan check box.
Personally I have little use for on-demand scans, for me that includes the Not so Smart Scan.
With a resident (on-access) scanner the need for on-demand scans is much depreciated. For the most part dormant/inert files are being scanned, the other active files are going to be scanned by the resident shields when they are activated.
Frequently it is going to find things that require a paid version to deal with that.