So far, I have delete the local account and recreate with the new password, reinstall Client OS, blacklist some unknown email sender from mailer-daemon report and block some ip (101.78.174.62 etc) with iptable. I think the broadcast messages has been stopped and I will check it for some day to make sure.
but I am not sure where is the spam source come from. I am not check the messages log yet, so I'll do it tomorrow.

Thanks for help Nick.