The situation where several employees were contacted by the same individual impersonating a recruiter best describes a spear-phishing campaign. Here's why:
Targeted Approach: Spear-phishing involves targeting specific individuals within an organization with personalized and convincing messages to trick them into divulging sensitive information or performing actions that compromise security.
Impersonation: The use of impersonation, in this case, a recruiter, is a common tactic in spear-phishing to gain the trust of the targeted individuals and increase the likelihood of a successful attack.
Correlated Contacts: The fact that several employees were contacted by the same individual suggests a coordinated effort to breach the organization's security by targeting multiple points of entry through social engineering.
References:
CompTIA Security+ SY0-601 Study Guide by Mike Chapple and David Seidl
NIST Special Publication 800-61: Computer Security Incident Handling Guide OWASP Phishing Cheat Sheet