W32/Mytob-BZ is a mass-mailing worm and backdoor Trojan that can be controlled through the Internet Relay Chat (IRC) network.

W32/Mytob-BZ is capable of spreading through email and through various operating system vulnerabilities such as LSASS (MS04-011).

W32/Mytob-BZ harvests email addresses from files on the infected computer and from the Windows address book.

More information can be found at this Sophos page.