AES modes:
ECB (identical blocks = identical ciphertext — insecure),
CBC (chains blocks with IV — needs padding, vulnerable to padding oracle),
GCM (authenticated encryption, no padding — preferred),
XTS (disk encryption).
Never use ECB. GCM is the modern choice — provides confidentiality + integrity in one pass (AEAD). CBC is acceptable but requires HMAC for integrity. XTS is specifically designed for disk sector encryption.