today i’ve learned that disabling trackback in wordpress’s settings > discussion [ ] Allow link notifications from other blogs (pingbacks and trackbacks) on new articles is not enough. your old posts, created before the date when this check-box was un-ticked, will still allow trackback which might be spammy.
solution? adjust the trackback setting on per-post level using the web interface or sql:
update wp_posts set ping_status='closed';