After trying various ways to stop spam such as captchas, abuse filters, blacklists and
whitelists. Some of which were intrusive, while others slowed the wiki down. I've now
had success with a mini Extension:ConfirmAccount. Setting this up is explained at
https://www.mediawiki.org/wiki/Extension:ConfirmAccount#Minimal_settings
Now instead any potential editor has to be approved manually, it only takes a moment if an
admin is watching the site. That is they request an account by confirming their email
address, providing a user name and a short message to prove they're not a bot.
Rob