Ransomware
Hostile software that locks your data or systems and bills you to get them back. Often also steals a copy first. Restore beats negotiation as a control.
Ransomware is a business model dressed as software: lock an organisation out of its own data or systems, then send an invoice. Modern crews usually steal a copy as well and threaten to publish. The encryptor is the impact. Entry is still identity, a vulnerable gateway, or a supplier.
Preparation that matters: privileged access hardened, EDR that actually isolates, backups the same credentials cannot toast, and an IR retainer that already knows your environment.
Paying is a legal and operational decision, not a security control. Have that conversation before the clock starts. ACSC can assist; they are not your restore vendor.
Fact source: ASD's ACSC glossary. Wording is Cyberstack's.