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?