Microsoft released a quick fix yesterday for a critical problem in its Internet Explorer browser and said a more permanent fix would be released tomorrow.
The problem is particularly dangerous because it can be exploited by creating a malicious website that attacks visitors who use a vulnerable browser. Those browsers include IE6, IE7, IE8 and IE9. The only version not affected is IE10.
The one-click fix will protect computers immediately, said Yunsun Wee, director of Microsoft's Trustworthy Computing group. Tomorrow, Microsoft will diverge from its normal patch schedule and issue a "cumulative update" for IE through its Windows Update service.
The cumulative update is named MS12-063 and will be released around 10am US Pacific Time. It will also address four other critical, remote code execution vulnerabilities, Wee said.
"We recommend that you install this update as soon as it is available," Wee wrote. "If you have automatic updates enabled on your PC, you won't need to take any action - it will automatically be updated on your machine. This will not only reinforce the issue that the Fix It addressed, but cover other issues as well."
Microsoft will hold a live webcast tomorrow to answer questions.
Microsoft normally issues patches on the second Tuesday of the month, but it issues an out-of-band update if a vulnerability is considered severe enough. The company said on Tuesday it had only seen a few attempts to exploit this vulnerability.
Security vendor AlienVault said it had discovered a second exploit using this IE vulnerability that installs a RAT (remote access tool) on victims' computers. The first exploit, found last weekend, installed a RAT called Poison Ivy.