hi Mike,
yes, it's a real danger. FTP is quite an insecure protocol. There are ways of securing FTP but they're icky.
But you're making a web app, so it's easy to allow users to upload files using the Upload Form Field type. See example 26. This uses HTTP not FTP, and then if you want secure it's just a case of flipping the switch to HTTPS.
Cheers
Bruce