Block server access from User-agent Libwww-perl. Botnet scripts that automatically look for vulnerabilities in your software are sometimes identified as User-Agent libwww-perl. By blocking access from libwww-perl you can eliminate many simpler attacks. This could also save your bandwidth quota by blocking certain bots or spiders from crawling your website.
This security fix to your site can help to prevent an automated script from defacing your website. Such defacement, which could include the disabling of interactive functions on your site, could damage your credibility and cause you to lose business.