I had that message too in one of my forums.
However of more concern over the last three days is that all of my forums are suffering registrations from spammers. (some I catch and ban on registration before the spam arrives.)
All have gmail addresses taking much the same form, a name and something else, usually a state/country, much interspersed with dots, such as:
ral.f.ric.her.d.s.au.s.tral.i.a@gmail.com
b.ob.m.a.rley.forevero.nly@gmail.com
r.al.fricher.d.s.a.ustr.alia@gmail.com
fr.a.nk.bi.ll.i.o.n.e.r.dol.l.a.r.s@gmail.com
f.r.a.nkb.il.l.ion.erd.o.lla.r.s@gmail.com
pe.tt.e.r.d.je.k.so.n.ar.iz.o.na@gmail.com
These are just some of them. I don't suppose there's a chance of capturing these and preventing them arrive at individual forums?
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.