Microsoft Urges Exchange Server Users To Install Emergency Patch Immediately KEY POINTS Hackers exploit four distinct zero-day vulnerabilities of the Exchange Server To prevent highly skilled hackers from exploiting the vulnerabilities of the Exchange Server, Microsoft has urged its users to install the recently released emergency patch as soon as possible. The update assumes significance as China-based hackers' group, Hafnium, recently used unknown exploits to hack a fully patched on-premise exchange server. Reports say that Hafnium is a state-sponsored, highly sophisticated threat actor. It conducts operations from leased virtual private servers in the United States and target entities in the country. Among its goals is to penetrate infectious disease researchers, law firms, higher education institutions, defense contractors, policy think tanks and NGOs, ARS Technica reported.