Floods a computer with requests until it shuts down and refuses to answer any requests for information. a ddos attack a polymorphic virus port blocking a trojan horse

A Distributed Denial Of Service (DDOS) floods a computer with requests from multiple sources (hence the "Distributed"). A computer has only a limited number of parallel requests it can handle, and if regular users are denied access because the computer is fully occupied, the DDOS is successful. Even worse is that the victimized computer shuts down.

Both shades should be exactly the same