Thread hijacking is a cyberattack technique where an attacker infiltrates an existing legitimate email conversation, often by compromising one of the participants’ accounts. The attacker then inserts malicious messages or links into the ongoing thread, making the communication appear trustworthy to recipients. This increases the likelihood that victims will open malicious attachments, click on phishing links, or disclose sensitive information. Thread hijacking is particularly dangerous because it leverages the established trust between correspondents, making detection more difficult. Organizations and individuals should be vigilant about unexpected messages, even within ongoing conversations, and use strong email security solutions to mitigate this threat.