Pseudoepigraphia is the name for it, or 'forgery' if you're more plain speaking.
Wikipedia Wrote:Pseudepigrapha are falsely attributed works, texts whose claimed authorship is unfounded; a work, simply, "whose real author attributed it to a figure of the past." The word "pseudepigrapha" (from the Greek: ψευδής, pseudēs,"lying" or "false" and ἐπιγραφή, epigraphē, "name" or "inscription" or "ascription"; thus when taken together it means "false superscription or title"; see the related epigraphy) is the plural of "pseudepigraphon" (sometimes Latinized as "pseudepigraphum"); the Anglicized forms "pseudepigraph" and "pseudepigraphs" are also used.