The unpatched bug in Internet Explorer 7 (IE7) that hackers are now exploiting also exists in older versions of the browser, including the still-widely-used IE6, Microsoft said late Thursday.
Friday, a Danish security researcher added that Microsoft's original countermeasure advice was insufficient, and recommended users take one of the new steps the company spelled out.
In a revised security advisory, Microsoft said research confirmed that the bug is within all its browsers, including those it currently supports -- IE5.01, IE6 and IE7 -- as well as IE8 Beta 2, a preview version the company doesn't support through normal channels.
Users running any of those browsers on Windows 2000, XP, Vista, Server 2003 or Server 2008 are at risk, Microsoft said.
Even so, the company continued to downplay the severity of the threat. "At this time, we are aware only of limited attacks that attempt to use this vulnerability against Windows Internet Explorer 7," said the advisory.
Microsoft also spelled out the root of the problem, saying that the bug is in IE's data binding functionality, and not, contrary to earlier reports by independent security researchers, in the HTML rendering code.
"The vulnerability exists as an invalid pointer reference in the data binding function of Internet Explorer," said Microsoft. "When data binding is enabled (which is the default state), it is possible under certain conditions for an object to be released without updating the array length, leaving the potential to access the deleted object's memory space. This can cause Internet Explorer to exit unexpectedly, in a state that is exploitable."
Microsoft also hinted that the "oledb32.dll" file contains the bug when it added recommendations that users disable or cripple the .dll's function as stop-gap measures. Oledb32.dll is a component of Microsoft Data Access, a collection of technologies for accessing different types of data in a uniform fashion. "OLEDB" stands for "Object Linking and Embedding, Database."
Danish security company Secunia claimed that its research, which it said has been passed along to Microsoft, identified the vulnerability's true nature. "After having published our initial advisory concerning this [zero]-day, one of my guys was therefore tasked with figuring out the exact nature of the problem," said Carsten Eiram, chief security specialist at Secunia, in a post to the company's blog early Friday. "It turned out that a lot of available information and assumptions were wrong."