Answer:
D. Trojan Horse.
Step-by-step explanation:
A Trojan horse is a kind of malware that is used to mislead computer users of its original intent. Most Trojan horses are usually not suspicious as they can come as an email attachment, advertisement etc. Immediately the user clicks the file or page, the attacker is able to have unauthorized access to the target network or the affected computer. This can further make the attacker have access to personal information.
This malicious actor who sent the file to several users on a companies network, just requires at least one of the computer users to execute the Trojan horse by clicking on the file, so the actor can have control inside the companies network.