The Commonwealth of Independent States (CIS) is a regional intergovernmental organization formed by several former Soviet republics after the dissolution of the USSR in 1991. In cybersecurity, CIS is significant because many malware strains are programmed to avoid infecting systems located in CIS countries. This is often done by checking system language or regional settings, allowing cybercriminals - who are frequently based in these regions - to evade local law enforcement. Understanding CIS is important for analyzing malware behavior and tracking threat actors' origins and motivations.