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.
Trojan.Agent.MSDGen is the generic detection based on the properties of a value under the following registry key which is indicative for Andromeda/Gamarue infections:
Worm.Gamarue is often dropped onto a system by exploit kits.
Malwarebytes protects users from Trojan.Agent.MSDGen by using real-time protection to block Worm.Gamarue.
Malwarebytes can detect and remove Trojan.Agent.MSDGen without further user interaction.