Petya ransomware is a type of malicious software that encrypts files on a victim's computer, making them inaccessible. It first appeared in 2016 and spreads through phishing emails or vulnerabilities in software. Once activated, it demands a ransom payment in Bitcoin to restore access to the files. Unlike traditional ransomware, Petya targets the master boot record, which is essential for starting the operating system. This means that even if the files are decrypted, the system may still be unusable. Organizations affected by Petya often face significant downtime and data loss, highlighting the importance of cybersecurity measures.