Microsoft releases software updates to plug four security holes that attackers have been using to plunder email communications at companies that use its Exchange Server products. The company says all four flaws are being actively exploited as part of a complex attack chain deployed by a previously unidentified Chinese cyber espionage group. The patches released today fix security problems in Microsoft Exchange Server 2013, 2016 and 2019. Microsoft said its Exchange Online service basically hosted email for businesses is not impacted by these flaws. Researchers at Reston, Va. based Volexity first spotted the attacks on Jan. 6, 2021.”]