The software described is classified as spyware because it monitors user activities and sends the information to an external source without the user's consent. This type of malware often leads to the symptoms mentioned, such as degraded system performance and unusual network traffic. Antivirus software typically protects against malware in general, which is not as specific as the correct answer. Adware is meant to serve ads to the user instead of monitoring behavior, while a Trojan is a type of malware that is disguised as legitimate software but performs malicious activities and does not specifically refer to the surveillance component that is central to spyware.