In its Security Intelligence Report (PDF), Microsoft said the In the fourth quarter of 2011 alone, Conficker was detected on 1.7 million systems worldwide, Microsoft said.
Why is Conficker's still so prevalent in organizations? Microsoft cites research that shows 92 percent of Conficker infections were a result of weak or stolen passwords, and 8 percent of infections exploited vulnerabilities for which a security update exists.
Conficker emerged in late November 2008, about a month after Microsoft pushed out an emergency patch for a critical vulnerability in Windows. Exploiting this vulnerability, the worm quickly spread to unpatched computers around the world, and one month later was followed up with a "B" variant.
"Conficker is one of the biggest security problems we face, yet it is well within our power to defend against," said Tim Rains, director of Microsoft Trustworthy Computing. "It is critically important that organizations focus on the security fundamentals to help protect against the most common threats."