What kind of attack did the Hacker attempt to carry out at the bank?

Bank of Timbuktu is a medium-sized, regional financial institution in Timbuktu. The bank has
deployed a new Internet-accessible Web application recently. Customers can access their account
balances, transfer money between accounts, pay bills and conduct online financial business using
a Web browser.
John Stevens is in charge of information security at Bank of Timbuktu. After one month in
production, several customers have complained about the Internet enabled banking application.
Strangely, the account balances of many of the bank’s customers had been changed! However,
money hasn’t been removed from the bank; instead, money was transferred between accounts.
Given this attack profile, John Stevens reviewed the Web application’s logs and found the
following entries:

What kind of attack did the Hacker attempt to carry out at the bank?

A.
Brute force attack in which the Hacker attempted guessing login ID and password from
password cracking tools.

B.
The Hacker attempted Session hijacking,in which the Hacker opened an account with the
bank,then logged in to receive a session ID,guessed the next ID and took over Jason’s session.

C.
The Hacker used a generator module to pass results to the Web server and exploited Web
application CGI vulnerability.

D.
The Hacker first attempted logins with suspected user names,then used SQL Injection to gain
access to valid bank login IDs.