Technology is disclosed for mitigating account enumeration and thus enhances network security. The technology can receive from a client computing device a sequence of characters corresponding to a portion of an email address input by a user. The technology retrieves a set of email addresses that have a common first portion identical to the received sequence of characters and generates hashed data. The hashed data is sent to the client computing device. A result value is then generated by hashing the input email address by using the same hashing function as the hashed data. If the result value is in the hashed data, the technology displays a text region for collecting from the user a password.