We fetch your site with Google's crawler user-agent and as a visitor, read the sitemap and look for spam in Google results. The full report goes only to someone who proves they own the domain.
Anyone can type any domain. If we showed results to everyone, the index would become a shopping list of easy targets. So the details go to the owner only.
Our notices come from [notice address]. We never ask for passwords, payment or a plugin install. If an email does, it isn't us.
Tell the owner, or report it to CERT Polska at incydent.cert.pl.
Add hackedindex-optout as a TXT record and we stop within 24 hours.