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.CLK is a detection for a certain type of Trojan that belongs to the Adware.Adclick family and infects Windows machines.
This family uses scheduled tasks to show user advertisements. It also collects information from the browser(s) and connects to an IRC server.
Trojan.Agent.CLK is offered at crack and keygen sites under various names to trick users into downloading and running it.
Malwarebytes protects users from Trojan.Agent.CLK by using real-time protection.
Malwarebytes can remove Trojan.Agent.CLK without further user interaction.