WordPress.org

Where are the settings

under: Settings > Search Antispam

CSS Hack

This option filters the most spam. Renames the name of the input field for search and makes an extra hidden with the old name. Checks than in with is text filled in.

Nonce Check

The Nonce check adds a nonce to the search field and check it.

DNSBL Check

The check uses a DNS lookup to opm.tornevall.org, ix.dnsbl.manitu.net and sbl/xbl.spamhaus.org Blacklists to check for known spammers IP's.

Referrer Check

Checks that the person comes form your blog.