Answer:
b. denial - of - service attack.
Step-by-step explanation:
Denial - of - service -
It is a type of attack , where the hackers tries to prevent the legitimate users from using the service .
The strategy used in this case is , the attacker sends a lot of messages or mails asking the network for authentication .
Hence , same is the case with Woori , it suffered from a denial - of - service attack .