Learn in the textbookTargeted Attacks and Phishing Scams
DefinitionAn interactive (correspondence-type) attack (やり取り型攻撃) is a targeted attack that first poses as a harmless inquiry and trades several emails, then sends a virus-laden file or similar once the other side has come to trust the sender.
ExplanationThe first email contains nothing malicious, so the staff member who receives it has no reason to be wary. After replying a few times, they take the sender for an ordinary inquirer and open the later attachment without suspicion. Contact-desk staff, whose job is to answer outside inquiries, are frequent targets.
AnalogyIt is like a con artist who does not push for a contract right away but chats a few times until you think "what a nice person", then brings up the real, crooked deal.