FTP ACCESS PROBLEM ON IIS4

Hello.

I have about 150 users that have access to their own personal folder on file server1. I have applied security permissions thus every user accesses only his/her personal folder.

The file structure on FILE server1 is as follows:

mainfolder
->userfolder1
->userfolder2
->userfolder3

In order to provide local LAN access I shared the mainfolder in order to make it viewable on the network neighborhood. Every user knowns where to find his personal network folder.

THE FTP PROBLEM
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The problems begun when I decided to give this functionality on the web. I configured my webserver's FTP service by creating virtual ftp directories for all my users 150. The procedure was simple.I just had to point the virtual directory for every user (say USER3) to the remote SERVER1's network user folder i.e. USERFOLDER3.

I thought that the problem was solved and that every user will access via FTP his personal folder but shortly reports begun to appear saying that users could access the folders of other colleagues.

For example user3 could access USERFOLDER2.

Any ideas what is going on and why the SECURITY permissions are not working on FTP. It looks like that only SHARING PERMISSIONS are applied.

How can overcome such a problem? How can I enable security permissions?

Is it a problem of the IIS4/FTP server?

If I move the folder structure locally on the webserver I think this will solve the problem. But, I need also to provide SHARING access when the users access my local area network. Can I have both LAN NETWORK SHARING ACCESS and FTP?

Thank you in advance.