Use of DNS Tunneling for C&C Communications

Network communication is a key function for any malicious program. Yes, there are exceptions, such as cryptors and ransomware Trojans that can do their job just fine without using the Internet. However, they also require their victims to establish contact with the threat actor so they can send the ransom and recover their encrypted data.

https://securelist.com/blog/research/78203/use-of-dns-tunneling-for-cc-communications/