There is no vulneability. POP3 antivirus is not developed for counteraction of trojan-downloaders. These actions are stopping by firewalls (for example, Kaspersky Internet Security 6.0: Anti-Hacker), proactive defence (Kaspersky Anti-Virus 6.0 and Kaspersky Internet Security 6.0: Proactive Defence) and file antivirus (Kaspersky Anti-Virus 6.0 and Kaspersky Internet Security 6.0: File Antivirus). Mail antivirus is working for protection of known mail clients, not for trojan-downloaders.
