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.DarkComet is a Remote Administration Tool (RAT) that has been around for a while, but we still find it in our telemetry.
Malwarebytes can remove this backdoor without further user interaction. A reboot is usually required after removal and Malwarebytes will prompt you to do so if necessary.