Block POSTs from blank referrers
I found a great article on Secure Computing: Sec-C that includes some excellent, simple Apache configurations and RewriteRules to blog various annoyances and compromises. A wonderful example is this bit, designed to stop POST requests that have no referrer set. There’s no reason for anyone to be trying to post arbitrary data to a script to not have a referrer, as that would indicate a direct hit — which is bad juju.
# Identify if a Referer is used
SetEnvIf Referer "^$" no_referer=1
Allow from all
Deny from env=no_referer
Lots of other fascinating security and forensics insights on the Sec-C blog as well!