By James Pearson LONDON (Reuters) – An Austrian firm which Microsoft said created malicious software that was detected on the computer systems of some of its clients in at least three countries has said its spying tool “Subzero” was for official use in EU states only. On Wednesday, Microsoft said the firm, DSIRF, had deployed the spying software, or spyware — capable of accessing confidential information such as passwords or logon credentials — at an unspecified number of unidentified banks, law firms and strategic consultancies. “Subzero is a software of the Austrian DSIRF GesmbH, which has…