I killed the running scan and started a new scan and now I have just one new issue displayed on the 'new issues' window:
* User "XXXXX" with 'subscriber' access has a very easy password.
but I received a wordfence alert mail concerning an other issue !?
* Modified plugin file: wp-content/plugins/dmsguestbook/dmsguestbook.css
I really don't understand what is the logic of that.