Provided is a process including: obtaining, with a domain controller of a private computer network, a set of user-authentication credentials comprising a first username and a first password; querying a distributed credential-monitoring application; receiving query results including one or more passwords associated with the first username; determining that at least some of the one or more passwords in the query results match the obtained first password; and in response to the determination, blocking, with the domain controller, access to a first user account on the private computer network associated with the obtained first username and first password.