Beginning in IS 6.5, the pub.client:ftp and pub.client.ftp:login built-in services support a new document parameter called secure. This document contains two fields used to control how IS connects to secure FTP servers
From the IS 6.5 Built-In Services Guide
You can also define SecureFTP (SFTP) listeners or ports so that IS services can be invoked upon receipt of files sent using FTP over SSL.
#webmethods-Protocol-and-Transport#Integration-Server-and-ESB#webMethods