HDBC's online banking website was knocked offline due to simultaneous login sessions established by a cyber attacker. What kind of attack was used?

The situation describes an online banking website being knocked offline due to simultaneous login sessions established by a cyber attacker, indicating a denial of service (DoS) attack. In a DoS attack, the objective is to overwhelm a target system or network, making it unable to respond to legitimate requests. By creating multiple login sessions, the attacker can exhaust resources and disrupt the availability of the service to legitimate users. This aligns with the characteristic of a DoS attack, where the primary goal is to deny service to users by flooding the system or exploiting vulnerabilities.

Other types of attacks listed, such as session hijacking, man-in-the-middle, and cross-site scripting, have different aims and methods. Session hijacking typically involves taking control of an active session without overwhelming the server. Man-in-the-middle attacks focus on intercepting or altering communication between two parties without necessarily impacting the server's availability. Cross-site scripting involves injecting malicious scripts into web applications, which again does not directly correlate with knocking a website offline. The key aspect of a DoS attack is its effect on the availability of resources, which is precisely what’s described in the scenario.