A few options: 1. They could force everybody with an old password to reset it. This would announce there was a flaw, but shouldn't be any riskier than having a

A few options: 1. They could force everybody with an old password to reset it. This would announce there was a flaw, but shouldn't be any riskier than having a "forgot password" link. 2. Silently upgrade passwords as users log in. This is risky, because many users might not log in for months. 3. Use their clusters to reverse weak password digests. This would be mostly transparent to customers, but runs a risk of accidentally locking out some customers. For example, if "bar" and "foo" both crypt() to "abcd123", and the user has password "foo", the recover-and-redigest method might change the password to "bar". 4. Wrap old passwords in a new digest -- presumably they have some way to determine which algo is used per-user. They could treat the output of crypt() as the input to a more secure digest, like scrypt, and then just store "crypt-plus-scrypt" in their database as the digest type.