>>use an ftp daemon that supports anti-hammering techniques.  Basically ban the
>>people for X minutes if they try to reconnect too fast.
> 
> 
> I use lukemftpd (aka tnftpd aka "The NetBSD ftpd" which is available for
> other operating systems like Linux). It can easily be configured for
> transfer rate throttling (for get/RETR and put/STORE) and limit concurrent
> connections by user (or class of users).
> 
> I don't think lukemftpd has a configuration to ban if connecting to often
> (and probably not needed if transfer rate throttling and concurrent
> connections limiting is used).

I look at it this way.  Teach the user at the other end some manners by banning 
them for a short, but growing time.  If they don't like it, well, find someone 
else's ftp server.  It is your machine and bandwidth and you are just trying to 
keep the service up for others to use.  Most ftp clients (even wget) can be set 
to pause for a set period of time before they retry.