A new employee logs in to the email system for the first time and notices a message from human resources about onboarding. The employee hovers over a few of the links within the email and discovers that the links do not correspond to links associated with the company. Which of the following attack vectors is most likely being used?

Social engineering is the most likely attack vector. The attacker is manipulating the new employee into clicking malicious links by impersonating a trusted source (Human Resources) and leveraging the employee's expectation of onboarding information. This type of attack preys on human psychology rather than technical vulnerabilities. Business email is too broad; while the attack uses email, "social engineering" describes the method of deception. An unsecured network might facilitate the attack but isn't the attack vector itself. Default credentials relate to authentication weaknesses, not the deceptive content of an email.