Ransomware is malware used to deny access to systems or data, usually by encrypting files and demanding payment for decryption. Many operations also steal sensitive information and threaten to publish it, so an attack can create both an availability crisis and a privacy or disclosure risk. Initial access may involve phishing, stolen credentials, exposed remote services, or exploitation of unpatched vulnerabilities; attackers may then move through the network before deploying the payload.
Defenses should combine vulnerability management, phishing-resistant authentication where practical, endpoint and network monitoring, and backups that are isolated from routine administrator access and regularly tested for recovery. Organizations should also limit privileges and segment critical systems to reduce the blast radius. An incident requires rapid containment, preservation of forensic evidence, restoration from known-good backups, and assessment of notification, legal, and regulatory obligations. Threat intelligence can help identify relevant criminal infrastructure or tactics, but it does not replace sound access control, patching, detection, and recovery practices.