Newsgroup spam is a type of spam where the targets are Usenet newsgroups. Usenet convention defines spamming as excessive multiple posting, i.e. repeated posting of a message or very similar messages to newsgroups. The spam may be commercial advertisements, opinionated messages, malicious files, or nonsensical posts designed to disrupt the newsgroups. A type of newsgroup spam is sporgery which is intended to make the targeted newsgroups unreadable. The prevalence of Usenet spam led to the development of the Breidbart Index as an objective measure of a message's "spamminess", and attempts to purge newsgroups of spam.