Microsoft issued its emergency patch for a vulnerability in all versions of Internet Explorer on Wednesday, eight days after first learning that attackers were seeding exploits for the flaw on a wide variety of Web sites.

The attacks accelerated over last weekend, climbing by more than 50 percent, according to estimates by the company. The flaw, which can be exploited remotely by malicious Web content, occurs in the way Internet Explorer handles memory for a specific function. The software giant rushed out a fix for the security issue in eight days, following its discovery that online criminals were using the flaw to attack Internet users.

"We initially learned the details on these attacks in the early morning hours of December 9th, and immediately activated off our Emergency Response process (SSIRP) to monitor the threat environment, fast track the product development and testing and to deliver guidance to customers," Mike Reavey, manager of the Microsoft Security Response Center, said in a post to the group's blog.

The response time shaved a day from the company's previous best time: Nine days to fix the a flaw in Windows' handling of files in the Windows media format (WMF). The flaw, which was discovered three years ago, allowed a specially crafted image file to compromise a Windows system that opens the image.

Security firms and researchers have estimated that thousands of Web sites have been compromised to host an attack targeting the vulnerability. One analyst controversially called for users to stop using Internet Explorer, at least until the fix came out.

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