Security researchers had identified a new worm, called Gimmiv, which exploited the vulnerability, and a hacker had posted an early sample of code that could be used to exploit the flaw on the Web.

Microsoft issued the patch more than two weeks ahead of its next security updates because the bug could be used to create an Internet worm attack and Microsoft had already seen a small number of attacks that exploited the flaw.

This vulnerability lies in the Windows Server service used to connect with other devices on networks. Although the firewall software that ships with Windows will block the worm from spreading, security experts are worried that the flaw could be used to spread infections between machines on local-area networks, which are not typically protected by firewalls.

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