Thank you, pd, that was really useful. I've had 2 comments like this (the other from David P who has already noted it on this thread). I was vaguely puzzled by both but didn't have the time to do anything, so didn't respond and then forgot about them. But I should have spotted that Erika's was a total fake - misspellings and zero followers. The David P one disappeared as you predicted. I've reported the 2nd one and am now alert to the issue thanks to your post.