When requesting SSH access to a remote system, a user accidentally emailed the id_rsa key to the administrator. Which of the following should the user do NEXT?

`ssh-add` manages keys in the SSH agent, and `known_hosts` stores public keys of remote servers; neither addresses the security compromise of a private key being exposed.

Setting `chmod 600 id_rsa` ensures proper local permissions but does not mitigate the fact that the private key was already transmitted insecurely and is potentially compromised.

Deleting the compromised private `id_rsa` key is part of the solution, but sending the *old* `id_rsa.pub` key is meaningless if the private key is compromised, and the immediate priority is to generate a new, secure key pair.

The `id_rsa` key is the private SSH key and must remain confidential. If it was accidentally emailed, it is compromised, and the user must immediately stop using it, revoke its access where possible, and generate a new SSH key pair with `ssh-keygen` to restore security.