I tried using Google Translate, which gave me "venenata libri", but when I tried to double-check this by translating this back into English it turned into "poisoned book", which is not what I want. "venenati libri" translates into "poisoned books", which is closer, but poisoned is still different from poisonous. Any suggestions?
Edited to clarify: yes, @Asteroides, I mean it in the sense of metaphorically noxious or harmful. Books that contain dangerous ideas.