The idea of having this plugin was that it would be a private site, just few a few people to whom I gave login details. I’ve reinstated the plugin, to test it again, and can’t see how people can register. Registration is turned off in General Settings. It was how these got themselves registered that was concerning me, and whether that might be a security issue.
I see that I need to post a support ticket with the owner, ZATZLabs, and that the plugin is not supported through www.remarpro.com. I also see that their support forum is not working due to a spamming problem, that the plugin hasn’t been updated for 10 months, and that it has not been tested with the latest version of WP!