Web shells are removed that wont to allow attackers to get access to MES (Microsoft Exchange Servers), the FBI has uncovered that some malware might remain. Hackers could still use this as backdoors into victim networks. Now, U.S. Justice authorities have initiated the removal of evil web shells from many computers running on-premises Microsoft Exchange Server software to work their corporate email services. These attacks began back in January and February of 2021 when various hackers discovered and exploited zero-day vulnerabilities in Microsoft Exchange Server software. The hackers took advantage of those vulnerabilities to lineup backdoors and gain persistent access to those servers, right up until they were caught in March of 2021. Even after the initial hackers came to light, more attackers searched for ways to attack following patching and publication of those vulnerabilities. While thousands of victims of this attack managed to get rid of these backdoors.