Thanks guys - with the advice that's been offered, I can now implement a solution with is as safe as it can be, considering the interface.

As regards the design of the interface - I had a little input into it, however, the developer of the software which runs on the remote machine had 'done this sort of thing before', and also claimed that no crc/md5 checking needed to be done because 'in [his] experience, ftp is a totally safe transport medium' - ah well, perhaps we can fix the interface with v2 ...

Pete