Well, got tempted and installed latest CIS.
Uninstalled previous version using Revo in advanced mode.
During installation, chose not to have the AV (Avast! for now), then got to the initial scan during setup.
It went fast until it reached C:\Windows and just stalled on the first file, _default.pif, so I clicked on Exit and the installation proceeded successfully.
Seems that _default.pif is a valid file but it did stop the scanning of the entire Windows directory.
BTW, is the AV installable in the future, without a new procedure?