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Enable reCaptcha and upgrade to Wishcraft X-Forum, then everyone registered or guest will be forced to fill recaptcha field too :)
Also check this thread -
https://xoops.org/modules/newbb/viewtopic.php?topic_id=74990&forum=20I usually avoid to use any 3rd party addons/services for protecting any of my sites using OpenSource CMS. HTACCESS is the best way to deal with spammers, check your CPanel logs (on HSP, not in XOOPS) for spammers IPs, then use Ip2 Country to detect them, and deny to whole country :)
The only one spammed so far remains phpFox but bcz the script is nulled and I use it only to complete translation, otherwise I don't need/keep any backdoors on my server opened....
May The Source Be With You!