Blacklist

It used to mean a list of people who are suspect or censured, and at one time was used to refer to Hollywood stars and writers who were blocked from working on movies during the 1950s because of anti-communist fear-mongering. Now it’s frequently used to describe the list of computers known to spew out unwanted spam e-mail. Any new, advanced spamming technique, however, threatens the effectiveness of using those computer blacklists.