To see how insecure a mode of operation can be, Wikipedia has a picture that was encrypted with ECB:
https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation...
https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation...
However ECB is a lot worse than "you can see data patterns"--with a chosen plaintext attack (very common scenario in networking and storage applications) any dumbass can decrypt it trivially.
No you can’t get decryption key using chosen plaintext attack with AES.
Read here: https://crypto.stackexchange.com/questions/1512/why-is-aes-r...