Campo is a spanish word meaning countryside, this word is referred in all URL this malware access, hence the name Campo. Campo loader is a simple and effective malware responsible for spreading other malware. It is known as the first stage payload for TrickBot, Gozi, and Zloader.
Buer is malware-as-a-service product that provide initial foothold in the victim's machine and deliver whatever payload it's owner what to deliver. It can be a RAT or Stealer. Recently it is know to be delivering ransomware like Ryuk.