HOWTO: ignore requests without user agent in Apache

A public web server could be reached by many http requests with no user agent. Apache can avoid this kind of requests. The configuration is very straightforward:

SetEnvIfNoCase User-Agent "^-?$" noUserAgent  
Order Allow,Deny  
Allow from All  
Deny from env=noUserAgent

In this example Apache ignores all requests without user agent that are directed to /path/to/a/directory

Comments are appreciate.