Yes, i have the same problem under win 8.1 64bit version. when including the file
http://www.m5stack.com/support/master/package_m5stack_index.json and trying to include this, an error message occurs: http://www.m5stack.com/support/master/package_m5stack_index.json Dateisignaturprüfung fehlgeschlagen. Datei ignoriert. Under win 8.1 64 bit vers. it is not possible to ignore the file verification.