How is ICMP used an exfiltration technique?

How is ICMP used an exfiltration technique?
A . by flooding the destination host with unreachable packets
B . by sending large numbers of ICMP packets with a targeted hosts source IP address using an IP broadcast address
C . by encrypting the payload in an ICMP packet to carry out command and control tasks on a compromised host
D . by overwhelming a targeted host with ICMP echo-request packets

Answer: C