There is considerable confusion when using the term "secure FTP". There are two different types of secure file transfer protocols available. edtFTPnet/PRO supports both.
Firstly, there is an enhancement to standard FTP (as defined in RFC 959), which uses the same FTP commands (and protocol) over secure sockets, i.e. over SSL/TLS. This is variously known as FTPS, FTP-SSL, and FTP-over-SSL. There are many FTP servers that support FTPS.
There is also another protocol, unfortunately known as SFTP, which also provides secure file access, but which is not related to the standard FTP protocol. This is implemented using SSH (Secure SHell), a suite of secure network connectivity tools (when used with SSH2 this is known as SFTP). The primary purpose of SSH is to enable users to remotely log into a machine over a secure connection. The two protocols are completely different and not related.
