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.
This is the generic detection based on the properties of a value under the following registry key, which is indicative for Andromeda/Gamarue infections:
Malwarebytes can remove Trojan.Agent.MSDGen without further user interaction. Note that it usually finds and removes Backdoor.Andromeda along with it.