They do it by hiring competent people, by following standardized accounting and security practices, by having third party auditing, etc. All those things that c

They do it by hiring competent people, by following standardized accounting and security practices, by having third party auditing, etc. All those things that companies like Mt Gox eschewed in the name of being able to rapidly push site updates without testing, etc. Yes, an environment with more stringent testing is less "fun," but at the same time, it's a lot more secure.