We are set up through Fiserv, so Fiserv handles security issues with the one company that is now generating credit entries only entering that data via a terminal at a company location. We are notified by Fiserv when a file has been received.
We have no intention to allow the generation of debit entries, so that issue has been been addressed. My opinion is that whatever entity system that you will be using that will allow a customer to originate ACH entries should have security built in, like dollar limits, number of entries per file, number of entries per week, verification of balances, multiple settlement dates, etc.
Actually, I'm happy its you and not me getting into this service as it could be risky.