The automatic update from Avast Free 17.7 to 17.8 silently installed the Avast Cleanup component (shown as Cleanup Premium in the Performance section). Cleanup was not installed before the update.
I have now seen this on two computers - the first time I assumed it was a human error - but the second time it was most definitly and un-authorised installation during the version upgrade.
This unexpected action appears to have also been reported for Avast Internet Security product during the same version upgrade - see here https://forum.avast.com/?topic=210865.0