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.Miuref is a family of Trojans that have different capabilities. The most prevalent objective seems to be click fraud.
Some variants alter search results to get the victims to visit the sites they promote. They also have the ability to download and run other malware.
These Trojans are usually installed by other malware, but they have also been spotted as email attachments.
Malwarebytes can remove this Trojan without further user interaction. Chrome users may have to manually delete an extension from their list of extensions, but the files will be removed by Malwarebytes.