Charlie, an ethical hacker, received a eccouncil video

Full Certification Question

Charlie, an ethical hacker, received a request to conduct a penetration test from the organization SecureCo. He initiates the reconnaissance phase and discovers an employee's email publicly available. Charlie devises a plan to send a deceptive email to this employee, altering the sender address to mimic the company's boss, "boss@secureco.com" . In the email, he urges the employee to promptly click on the "report link" for verification. Falling for the ruse, the employee opens the link, unknowingly compromising their computer. Through these tactics, Charlie gains unauthorized access to the corporate network, successfully completing the penetration test. What type of attack did Charlie use?