Trojan.Agent refers to a generic Trojan malware detection. It is used for detections that are either associated with no specific malware families or not enough information is available to pinpoint the malware family.
Backdoor.Agent.PGen is a generic detection for backdoors that use the following specific registry keys to gain persistence:
Currently, DarkComet variants predominantly use these keys.
Malwarebytes can remove this threat without further user interaction. It is recommended to do a full system scan since this backdoor may have been used to install more malware on the system.