BLD stands for "black list daemon" and is intended to build blacklists
using simple rules based on a maximum number of submissions of the same
IP address during a minimum time interval.  BLD was primarily designed to
fight against dictionnary-based spams (by making the MTA report to BLD
any host that tries to send a mail to an unknown user) but can be used
by any application that needs a blacklist based on connection rate limits.

IMPORTANT!
    This software is in early development stage.  It is stable but still
    lacks some features.  As of now, it is highly recommended to USE IT IN
    A SAFE ENVIRONMENT: access control is based on clients IP addresses.
    This is why, by default, BLD binds to localhost and should not accept
    requests from a machine where non-trusted users can be logged in or
    establish network connections to via other means (PHP for example).

BLD uses a very simple algorithm to decide whether to add IP addresses to
the blacklist or not.  The first time an IP address is submitted, it
is added to an internal list with a timestamp and all further requests
increment a counter for this IP.  As soon as the minimum time interval is
elapsed (default: 30 seconds), and if a maximum requests ratio is reached
(default: 10 submissions in the 30 seconds interval), the IP is put in
the blacklist.  It is then blacklisted for a configurable time (default:
900 seconds).

BLD has been written by Olivier Beyssac <obld@r14.freenix.org> and is
released under the BSD license.  Its home page is at
http://www.online.redhate.org/bld/

Many thanks to:
Pierre Beyssac <pb@fasterix.freenix.org> for his fixes
Jean-Marc Drouaud <jm@drouaud.com> for his advices.

And also to the following contributors:
Samuel Tardieu <sam@rfc1149.net>
