The dangerous Internet Explorer attack code used in last month's attack on Google's corporate networks is now public.

The code was submitted for analysis Thursday on the Wepawet malware analysis Web site, making it publicly a vailable. By Friday, it had been included in at least one publicly available hacking tool and could be seen in online attacks, according to Dave Marcus, director of security research and communications at McAfee.

The attack is very reliable on Internet Explorer 6 running on Windows XP, and it could possibly be modified to work on more recent versions of the browser, Marcus said. "The game really changes now that it's hosted publicly," he said.

A hacker could use the code to run unauthorized software on a victim's computer by tricking them into viewing a maliciously crafted Web page.

That's apparently what happened at Google late last year, when hackers were able to get into the company's internal systems. According to people familiar with the incident, 33 other companies were also targeted by the attack, including Adobe Systems.

On Thursday, Symantec and Juniper Networks said they were investigating the incident, and Yahoo, Northrop Grumman and Dow Chemical have also been named as victims in published reports.

Microsoft issued a security advisory on the IE flaw Thursday and has not ruled out the possibility of rushing out an emergency "out-of-cycle" patch to fix it. Microsoft's next set of security patches is due Feb. 9, giving hackers more than three weeks to exploit the flaw.

Security researchers say it would be very hard to exploit the flaw reliably on Windows Vista or Windows 7 systems, however, because of their advanced memory protection technology.

Marcus said that, judging from the amount of concern McAfee is hearing from corporate customers, an out-of-cycle patch is a strong possibility. "My gut tells me that they're going to go with an out-of-cycle," he said. "It's too good of a vulnerability for most of the bad guys to overlook."

The problem is serious enough that on Friday, Germany's federal IT security agency, the Federal Office for Information Security, advised users (in German) to use an alternative browser until Microsoft fixes the issue.

McAfee has more details on the attack here.