COMPUTER SECURITY SYSTEM WITH MALICIOUS SCRIPT DOCUMENT IDENTIFICATION

In some implementations, a method performed by data processing apparatuses includes receiving a new script document in a scripting language that has not yet been classified; identifying features of the new script document, wherein at least some of the features are script-language commands contained in the new script document; generating first feature-data for the new script document, the first feature-data comprising measures of frequency of occurrences of the features within the new script document; and assigning a classification to the new script document based on a comparison of the first feature-data with training data that comprises second feature-data for known-malicious script documents and third feature-data for known-benign script documents.