FTP Security - Repeated Login Attempts

Question

Over the past 2 weeks or so, i've seen about a bazillion of these types of entries in the system log of one of our ftp servers:
Aug 21 03:39:22 ns ftpd[4099]: ACL Check failed for Administrator
Aug 21 03:39:22 ns ftpd[4099]: ACL Check failed for Administrator
Aug 21 03:39:22 ns ftpd[4099]: ACL Check failed for Administrator
Aug 21 03:39:23 ns ftpd[4099]: repeated login failures from atlantis @ 83.143.18.134 [83.143.18.134]
Obviously, someone is trying to gain access (unsuccessfully - thank goodness) to the system. The repeated login attempts last anywhere from 5 - 30 minutes, always with the username Administrator. The IP addresses are from all over the world - Europe, Asia, and the US. Why we have a bullseye on us all of a sudden is unknown. This server has been running for close to three years now, and I've never seen attempts with this frequency.
The Administrator user doesn't have ftp access on this system, so I'm not too worried about these break - in attempts. (Or should I be?)
My formal question is this - is there anything that can be done with the out of the box ftp server to deter these attempts, or at least block attempts by IP address temporarily after several failed logins?
What approach have others used? Is it time to start looking at another ftp server software package that has more security settings?
Any help / input would be appreciated.
I miss my Apple IIc   Mac OS X (10.4.6)  

Answer 1

Thanks for the feedback Camelot. I'll post my replies under the quoted text below.
If you're running a public server you're going to get
hits you don't want. Fact of life.
Script kiddies around the world are going to try
whatever username and password they can think of to
log into your server.
Having a different FTP server isn't going to change
that - any other server is just as vulnerable to
brute-force attacks as the built-in server. How do
you think a different server is going to react any
differently?
I don't know - that's why I asked.
I've only used the bundled ftp server with OS X server. I was wondering if there was a ftp software package that temporarily blocked IPs after 'n' number of invalid login attempts or something like that. And thought I'd see if anyone had any experience in this department.
Your only safeguards are some combination of:
1) use your firewall to restrict access to the server
to known/trusted IP addresses
Unfortunately, a few of our users use dynamic IPs. Which is a bummer.
2) use a VPN to connect to the server, then connect
to the internal address
We've used this method successfully before. We might go back to it...
It was a 'pain' for some of our remote users and I finally gave into the nagging to do away with it because I spent way too much time providing phone support for remote users. I know, I know, it's just laziness on my part.
3) use a different protocol that supports public key
authentication (and turn off password
authentication), e.g. SFTP.
I've looked into SFTP for the OS X ftp server on these boards and most discussions don't seem to resolve into a definitive solution for implementing SFTP on the OS X server. Anyone get this working properly? I'd love to set it up to support SFTP only and disable password authentication.
I'm leaving the original question open - I'd like to know if there is ftp software that works well on OS X server that would temporarily block an IP after 'n' invalid attempts, or has something similar.
Or for someone to tell me I'm just being paranoid - and that the current setup should be OK.