"We have seen speculation that Microsoft might release an update for this issue out-of-band," said Jerry Bryant, a senior manager with the Microsoft Security Response Center (MSRC), referring to the term the company uses for a rush fix. "I can tell you that we are working hard to produce an update which is now in testing."

Microsoft of the vulnerability in IE6 and IE7 last Tuesday when it said hackers were exploiting the bug. The next day, Israeli security researcher Moshe Ben Abu grabbed the attack code from a site that had been using it to conduct "drive-by" attacks, then , which he published to the popular Metasploit penetration testing framework.

Even before Abu posted his exploit, experts had said they expected to ship an out-of-band update if attack code went public.

Bryant, however, did not commit Microsoft to an emergency patch, saying only, "We never rule out the possibility of an out-of-band update," in an entry on the Friday. Testing, he added, was a "critical and time intensive" part of the process because Microsoft had to confirm the update worked with all versions of both IE and Windows. Only IE6 and IE7 harbor the bug; the oldest and the newest editions, IE 5.01 and IE8 respectively, do not.

Also yesterday, Microsoft offered an automated to disable the component in the "iepeers.dll" file that contains the . The free tool works on machines powered by Windows XP or Windows Server 2003. That workaround was an addition to those that Microsoft recommended last Tuesday, which included disabling scripting, enabling DEP (data execution prevention) and .