The latest attacks are coming courtesy of a new variant of the Conficker worm, identified by Microsoft as Win32/Conficker.B. According to the company, the variant is hitting machines that have not applied the fix, while also spreading via network shares by attempting to log in to machines using a list of weak passwords.

The worm exploits a vulnerability caused by the Server service failing to properly handle specifically crafted RPC (remote procedure call) requests. If an exploit is successful, it could allow an attacker to execute code remotely when file sharing is enabled.

The issue was the subject of a rare out-of-band security patch by Microsoft on Oct. 23. As attacks mounted, Microsoft issued a follow-up advisory on its Security Response Center blog a month later.

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