This is the name of the most recent virus the Anti-Virus engine caught specifically in POP3 traffic. A detection here specifically means a user's POP3 mail client was in the process of downloading an infected message, distinguishing it from an SMTP-side catch that happens before the message is even delivered to a mailbox. For example, this field naming a malware variant caught as a specific user's mail client retrieved messages from an external POP3 mailbox.