Don't you think there should be a system in place that prevents you from making that size of a purchase without jumping through some serious hoops? In the computing world we have "Are you sure you want to replace XYZ File?", so at an absolute bare minimum wouldn't you expect a trader to see a warning that looks something like "Are you sure you want to invest $1billion? (or did you totally f*ck up and mean to invest $1million?)".