A quarantine method and system for allowing a client terminal to connect to a user network. An authentication apparatus recognizes that a communication means of the client terminal has been activated. The authentication apparatus confirms a common certificate for the client terminal. An Internet Protocol (IP) address is provided to the client terminal to enable the client terminal to log in to the quarantine network. A first authentication server security checks the client terminal to determine whether each check item of at least two check items has a violation. The client terminal is allowed to connect to the user network, via a second authentication server confirming a user certificate for the client terminal followed by the second authentication server storing the user certificate in the client terminal. The security measure server, the first authentication server, and the second authentication server are physically distinct hardware servers.