I have lost control of my site because of this plugin

I have installed this plugin on my shopping site to update to a new product range and it was working for a while.
Than suddenly, as I was working in the site’s admin I was logged out. When logged back in, the ‘site under maintenance’ screen come up and since than I could not access the admin area at all.
I have posted a support message but even after 10 hours no reply received from the author(s). It turned out that even the admin credentials were compromised somehow, so I have obviously deleted this plugin and now everything is back.
I do not recommend using it.