WordPress.org

This WordPress plugin investigates web requests with simple WordPress-specific heuristics to identify and stop most obvious attacks. There exist a few powerful generic modules that do this; but they're not always installed on web servers, and difficult to configure.

It intelligently whitelists and blacklists pathological-looking phrases based on which field they appear within in a page request (unknown/numeric parameters vs. known post bodies, comment bodies, etc.). Its purpose is not to replace prompt and responsible upgrading, but rather to mitigate 0-day attacks and let bloggers sleep better at night.

See: WordPress Firewall Info and WordPress Firewall Security Filters for more information.