A Taiwanese computer security researcher indicated on Friday that exploit code he developed and privately shared with Microsoft ended up in hostile hands. The Wall Street Journal reports that Microsoft shared data on the Exchange flaws with MAPP partners on Feb. 23. Microsoft is now investigating whether one of its partners is at fault. The vulnerability was used to attack tens of thousands of Exchange email servers before Microsoft deployed software patches on March 2. A fierce flurry of worldwide attacks ensued between Feb. 26 and March 3, 68,000 distinct IPs were compromised, according to The Shadowserver Foundation.”]
Source: https://www.cuinfosecurity.com/blogs/how-did-exchange-server-exploit-leak-p-3005