Imagine a scenario in which you want to repay a friend who bought you lunch, by sending money online to his or her account. There are several ways in which this could go wrong, including: The financial institution could have a technical issue, such as its systems are down or the machines aren’t working properly. Your or your friend’s account could have been hacked—for example, there could be a denial-of-service attack or identity theft. The transfer limits for your or your friend’s account co...