What type of malware is likely being countered if it copies itself to workstations through a shared fileshare?

The appropriate type of malware in this case is a worm. Worms are designed to replicate themselves and spread autonomously across networks and connected devices, often exploiting shared resources such as file shares. When a worm copies itself to workstations, it can do so without needing any human interaction, making it particularly efficient at spreading quickly through networks.

While viruses do require a host program to activate and replicate, they typically need user action to spread, such as opening an infected file. Therefore, they spread in a more limited way compared to worms. Trojan horses disguise themselves as legitimate software but do not self-replicate; instead, they rely on users being deceived into installing them. Spyware is designed to gather information without the user's knowledge and doesn’t spread like a worm or virus.

Thus, when considering the characteristics of each type of malware, the action of copying itself through a shared fileshare aligns most closely with the behavior of a worm, as it takes advantage of network vulnerabilities to propagate independently.