What is ransomware, and why is it considered the top data threat?

Question

Accepted Answer

Ransomware is extortion malware: it blocks the PC or encrypts/deletes data and only restores access after a ransom is paid.
The owners of infected machines are extorted — typically the PC is locked or files are encrypted, and a payment (usually in cryptocurrency) is demanded for the decryption key.
Why it's #1 (per ENISA 2024): it converts an intrusion into money quickly and at scale, and modern variants hit multiple CIA goals:

Availability — your files are locked
Confidentiality — data is often stolen first (see "double extortion")
Integrity — systems are tampered with

Defence that actually works: tested, offline/immutable backups — so you can restore without paying. (Though backups alone don't stop the leak in a double-extortion attack.)
Tip: Paying is discouraged — it funds the ecosystem and doesn't guarantee you get a working key or that the stolen data is deleted.