I remember a conversation back in 1995 or 1996 with someone who described to me how the Automated ClearingHouse (ACH) for checking worked. He explained that once you had an ACH merchant account, you sent in a message of roughly the form (src, dest, amount, reason) and money got moved. I argued with him that this was inconceivable (yeah, yeah), and he must be mis-understanding. He assured me that no, he was right, and that the reason they ran this way was because it was cheaper, and because only trustworthy people could get ACH merchant accounts.
Fast forward a few years, to a fellow who sends out cheques for bugs:
Leading banks and investment funds have been foundering, because of bad debts and lack of trust; and other, less well-known kinds of fiscal chaos are also on the horizon. For example, due to an unfixable security flaw in the way funds are now transferred electronically, worldwide, it is no longer safe to write personal checks. A criminal who sees the numbers that are printed at the bottom of any check that you write can use that information to withdraw all the money from your account. He or she can do this in various ways, without even knowing your name — for example by creating an ATM card, or by impersonating a bank in some country of the world where safeguards are minimal, or by printing a document that looks like a check. The account number and routing information are all that international financial institutions look at before deciding to transfer funds from one account to another. (Donald Knuth, “Financial Fiasco.”)