Indian security researchers have released proof-of-concept code that can be used to take over a computer running Microsoft's upcoming Windows 7 operating system, despite earlier promising not to make the code public for fear it could be misused.

VBootkit 2.0 was developed by researchers Vipin Kumar and Nitin Kumar and is now available for download under an open-source license.

They unveiled the proof-of-concept code at the Hack In The Box (HITB) security conference in Dubai last month, where they showed how it could be used to give an attacker complete control over a Windows 7 computer, including the ability to remove and restore user passwords without a trace and strip DRM (digital rights management) protections from media files.

"We don't have any plans to make it open source, due to chances of misuse," Nitin Kumar wrote in an April 27 e-mail.

In an e-mail announcing the release of the VBootkit 2.0, Vipin Kumar did not offer a reason for their apparent change of heart. But in a follow-up message, he said they wanted to help spur other researchers to develop new defenses against these types of attacks.

"All we are trying to do is help more people understand the real enemy, malware, so new innovations can occur," Vipin Kumar wrote.

Microsoft doesn't consider VBootkit 2.0 a serious threat. "Any claims made at the event relating to Windows 7 having a security vulnerability are not true," the software maker said in an e-mail statement.

Microsoft's assertion is technically true. VBootkit 2.0 does not exploit a security vulnerability. Instead, it exploits a design flaw in the operating system, which assumes that the boot process can be trusted and is safe from attack. VBootkit 2.0 works by modifying files as they are loaded into the main memory of a computer, a type of attack that Windows 7 is not designed to stop on its own.

This type of attack can be blocked by using BitLocker Drive Encryption (BDE) and a Trusted Platform Module, but these features will not be available on many Windows 7 computers.

Microsoft also cited the nature of the VBootkit 2.0 demonstration as further evidence that it doesn't present a threat. "With the scenario we have seen reported there is no question of Windows 7 being broken into or comprised remotely -- by an attacker using a malicious exploit over the Internet for example," Microsoft said.

However, VBootkit 2.0 is only a proof of concept, meant to illustrate that an attack can work. The code can be modified by an attacker and used for a remote attack, as has been done with other bootkit attacks, Nitin Kumar said.