FTP service suffers brute force password attack

one Win2k server has two FTP services activated, one of which is on the default port 21 and has recently been attacked by brute force password.
the Windows Event Viewer prompts the following message:
evevent type: Warning
event Source: msftpsvc
event category: None
event ID: 100
date: 20/02/2006
time: 3:06:33 a.m.
User: N/A
Computer: abcfp1
description:
the server was unable to logon the Windows NT account 'admin' due to the following error: logon Failure: Unknown user name or bad password. the data is the error code. ent type:

by viewing this information, it is found that the attack frequency is 5-6 times/second, only the Program can achieve the frequency
for Win2k systems, there are usually administrator users, but it will be valid.
countermeasures:
you cannot change the name of a Super User, so you can only increase the password strength of the Super User.
In addition, configure the number of FTP service connections in IIS, no more than 2, reducing the attack frequency of the other Party
hope that the other party's patience is limited, or the time is limited, it is difficult to leave