Black Arrow Cyber Threat Briefing 19 March 2021: Tens Of Thousands Of Microsoft Exchange Customers Under Attack, Targeted By Multiple Hacker Groups; Over $4.2 Billion Officially Lost To Cyber Crime In 2020; Cyber Attacks Multiply On HNWIs; Largest Ransomware Demand Now Stands At $30 Million; 71 Percent Of Office 365 Users Suffer Malicious Account Takeovers; More Than 16 Million Covid-Themed Cyber Attacks Launched In 2020; Cyber Now Key To National Security;