I prodded the LJ staff about the recent security incident and received the following response to my suggestion that they warn the user:

We understand your concern in this matter. However, we generally do not contact users to inform them of a possible threat to their account security. There are several safeguards in place to help protect users’ accounts, including various rate limits, but ultimately it is the user’s responsibility to ensure that their account remains secure.

We regret that we will be unable to assist you in this matter.