The drinks supplier became aware of the incident on Friday and shut down all of its IT systems.
It has also engaged a forensic information technology firm and legal counsel to investigate and restore its system as quickly as possible.
C&C Group continues to operate as normal.
Due to COVID-19 restrictions, MCB is operating at reduced volumes and is temporarily supporting customers and suppliers manually while IT systems are being restored.
MCB is in the process of informing its customers and suppliers of the incident and the actions the company is taking and has notified the relevant authorities, including the Information Commissioner’s Office.