Date: 03/17/05 (Java Web)    Keywords: spam

It was surprising to find no comment spam after installing WordPress 1.5, noting that I haven't enabled CAPTCHA with this upgrade. However I soon realized that I wasn't receiving any normal comments too on very commentable articles. I realized yesterday the culprit was this option in WordPress: Blacklist comments from open and insecure proxies. [...]

Source: http://blog.taragana.com/index.php/archive/all-comments-get-nuked-by-blackhole-option-on-blocking-open-proxy-lists-in-wordpress-15-strayhorn/