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.Zapchast is Malwarebytes’ detection name for a family of Trojans that installs an mIRC client on the affected system.
Backdoor.Zapchast allows the threat actor to take control of the affected system. They often deploy a keylogger given this chance.
These Trojans are spread by email as attachments most of the time.
Malwarebytes protects users from Backdoor.Zapchast by using real-time potection.
Malwarebytes can remove Backdoor.Zapchast without further user interaction.
You may find additional malware if this Trojan has been active.