From Share and share alike? Not Quite, by Mike Mimoso at Threatpost:

“With retail, the challenge is that most of the companies we share with are direct competitors,” Phillips said. “From a security perspective, you have to get over that and share because we’re all facing the same challenges. There’s no way any of us will win the war on our own.”

If sharing information on attacks provides your competitors a business advantage, you have serious issues unrelated to security.