By James Pearson LONDON (Reuters) – Security researchers at Microsoft have said an Austrian firm was behind a string of digital intrusions at banks, law firms and strategic consultancies in at least three countries. The firm, DSIRF, developed spyware – malicious software designed to spy on or steal information from a target’s device – called “Subzero” which uses so-called Zero-day exploits to access confidential information such as passwords, or logon credentials, Microsoft said in a blog post on Wednesday. “Observed victims to date include law firms, banks, and strategic consultancies in coun…