Security Setting of ftproot directory

We are downloading antivirus signature file from web to
FTP Server. When users login, clients will automatically
download the updated signature file from the FTP Server.

However, we would like to find out the best way of
downloading the signature file from web to the ftproot
directory.

Should we just map to the E$ and copy the signature file
across OR create a share for the ftproot directory. If
share is preferred, what security setting should we give
to administrators ? Just write and read ?

Thanks