The noun black list (or blacklist), a list of people or things that are deemed unsafe or undesirable, has been in the language since the early 1600s. The verb form (meaning to place on a black list) first showed up in the early 1700s. Today's new verb comes from the noun white list (or whitelist) which entered the language around 1900. The verb form (to place someone or something on a list of things deemed safe or acceptable) has been around since about the mid-70s. The specific sense of placing items on a list of things known not to be spam or viruses first started appearing in Usenet posts around 1996, although, as the earliest citation shows, the verb didn't make it into the media until 2001.