I've written about how to keep secrets before. I noted that most people reveal secrets because they seek a sanction or approval for being what they are, and for the things they did. And so for individuals, keeping secrets means to seek no sanction for being what you are and no approval for it.
However organizations are different. Most whistle blowers, are so because they seek a moral high ground above the organization and are willing to delay gratification for this higher ground. It is this moral drive that drives them to betray their group.
There is a well known quote by Antoine de Saint-Exupery:
“If you want to build a ship, don't drum up people together to collect wood and don't assign them tasks and work, but rather teach them to long for the endless immensity of the sea”
So to keep secrets in an organization you have to develop within its members a longing and the necessity to keep secrets. For instance consider Rennaisance Technologies, the secretive hedge fund, which has not revealed anything about its operations, while claiming to have an open culture within it open for all to modify and change. Such an atmosphere is only possible if there is a longing and a reason why the secrets must be kept.
I would hypothesize that James Simons, would even have deduced a reason why his methods will not work once the entire market knows about it. Inefficiencies he discovered would not exist if everyone used it. Every employee would know this. And it is this knowledge that drives the secret.