The new default password-based authentication mechanism in MongoDB 3.0 is SCRAM (Secure Password Authentication for Remote Clients), designed to counter the threat-model of eavesdropping, replaying, and a malicious server. SCRAM resists eavesdropping by using client-side entropy to derive the ClientKey, while also requiring a high iteration count to slow down dictionary attacks. Resistance to replay is achieved through the use of random nonces in each instance of the protocol. A malicious server can be prevented from impersonating a legitimate one by verifying the ServerSignature at the end of the SCRAM session. However, if an attacker gains access to a server's stored credentials and also eavesdrops on an instance of SCRAM, they will be able to learn the ClientKey without performing a dictionary attack. To mitigate this risk, it is recommended to use Transport Layer Security (TLS) in conjunction with SCRAM. MongoDB 3.0 users can easily switch from MONGODB-CR to SCRAM by running the `authSchemaUpgrade` command.