libwww-perl is an otherwise good tool that is being used by hackers to look for sites with vulnerabilities. From the hits I get, they try to see if my site has a script that is prone to hacking, but I don't have it installed. After doing some research, I read about blocking access from those bots by putting this in .htaccess:
SetEnvIfNoCase User-Agent "^libwww-perl*" block_bad_bots
Deny from env=block_bad_bots
It's working. In my error log, I see access to suspicious folders being denied, and the latest visitors log shows that user agent is getting a 403 Forbidden error code.