Petya is a malware family first discovered in 2016 that targeted Microsoft Windows systems. The original Petya strain encrypted key disk structures (such as the master file table), blocked normal boot, and demanded a Bitcoin ransom. Early Petya campaigns were distributed through phishing emails that delivered malicious attachments. Later variants evolved in delivery and behavior. In 2017, the NotPetya outbreak spread through a compromised update mechanism for Ukrainian accounting software (MeDoc) and then moved across networks using the EternalBlue exploit and credential-based lateral movement tools.