Here at WP KickStart, we go through many plugins every week, and every project. Some a site specific, some we build our selves but one is a simple tool we use every project. This plugin is called: Block Bad Queries (BBQ).
Rather than reinvent the wheel the authors website describes the plugin as:
” a simple script that protects your website against malicious URL requests. BBQ checks all incoming traffic and quietly blocks bad requests containing nasty stuff like
base64_, and excessively long request-strings. “
Put simply; it stops the bad stuff!