Rootkit.Fileless.MTGen is the generic detection for fileless infections that use a rootkit to hide their presence. In the majority of the cases, they use registry keys that are designed to run Powershell commands that carry out the rest of the infection. Other than Powershell, we have also seen the mshta command.
Malwarebytes protects users from Rootkit.Fileless.MTGen using real-time protection to block the trojans that install these rootkits.
Malwarebytes can detect and remove Rootkit.Fileless.MTGen without further user interaction.