Albrecht Has Noticed a Number of Clients on the Network

Albrecht has noticed a number of clients on the network attempting to contact the same external IP address at a constant rate of once every five minutes over the past 72 hours. Which of the following might be the cause of his concern?

A) The computers are currently taking part in a DDoS attack against the destination IP address.
B) The computers may have formed a distributed computing configuration that allows them to work as a single command and control system.
C) The computers may be infected with malware that has made them part of a botnet.
D) The computers are performing a port scan against a victim computer.