LogFormat "%a" problem
CustomLog "|/path/to/this/script.pl" problem

##</code><code>##

#!/usr/bin/perl -w

$|=1;

use strict;
use Fcntl qw(:DEFAULT);
use Net::Netmask;
use Net::Whois::IANA;
use Proc::Fork;
use SDBM_File;

my $iana = Net::Whois::IANA->new;

my $bye  = join '|', (
 'strings known to occur',
 'in custname and orgname',
);

tie (my %seen, 'SDBM_File', '/some/sdbm', O_RDWR|O_CREAT, 0666)
or die "$!";

open my $fh, "< /dev/stdin" or die "$!";
while (<$fh>) {
  chomp;
  next if exists $seen{$_};
  $seen{$_} = 1;

  my $ip = $_;

  child {
    my $problem = 0;
    my $host = `host $ip`;
    $problem = 1 if $host =~ /some host name regex/;

    if ($problem or $host =~ /not found/) {
      $iana->whois_query(-ip=>$ip);

      my $inetnum  = $iana->inetnum || '';
      my $custname = $iana->{QUERY}->{custname} || '';
      my $orgname  = $iana->{QUERY}->{orgname}  || '';

      next unless $inetnum and ($custname or $orgname);

      if ($custname =~ /$bye/i or $orgname =~ /$bye/i){
        my $mask = Net::Netmask->new($inetnum);
        `iptables -A INPUT -s $mask -j DROP`;
      }
    }
  }
}
close $fh or die "$!";
untie %seen;