W32/Rbot-MI is a worm that attempts to spread to remote network shares. It also contains backdoor Trojan functionality, allowing unauthorized remote access to the infected computer via IRC channels while running in the background as a service process.

W32/Rbot-MI spreads to network shares with weak passwords as a result of the backdoor Trojan element receiving the appropriate command from a remote user.

More information is at this Sophos page.