Methods, systems, and apparatus, including computer programs encoded on computer storage media, are described for identifying target terms, e.g., spam terms within a collection of documents. In one aspect, methods can include identifying spam terms by calculating a blacklist term frequency-inverse document frequency (BTF-IDF) score for multiple terms, and by selecting, as the spam terms, the terms that have scores above or below a threshold score. The multiple terms may be derived from documents that are associated with accounts that have been designated as spam accounts.