Answer:
Worms ( D )
Step-by-step explanation:
Worms in computer systems spread over the system by taking advantages of the operating system of the computer they found themselves because most operating system have some vulnerabilities.
These worms which are a type of malware affects the computer systems by overloading the servers and consuming more than necessary bandwidth from the network it is found.
worms sometimes contain payloads which might damage the computers in which they are found. spyware causes the slow loading/running of system operations because it is a malware that hogs system resources.