Microsoft has failed to fix an Internet Explorer vulnerability that could give hackers control of people's computers before details of it went online.
The zero-day exploit - details of which are now on the web - means hackers can use phishing attacks to lure PC users to a malicious website that would effectively let hackers take over the victims' computers.
Microsoft was made aware of the flaw in October after a Belgian researcher, Peter Van Eeckhoutte, discovered it.
But it did not fix the weakness before details of the flaw were made public by HP's Zero Day Initiative (ZDI) yesterday.
ZDI's disclosure read: "This vulnerability allows remote attackers to execute arbitrary code on vulnerable installations of Microsoft Internet Explorer. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file.
"An attacker who successfully exploited these vulnerabilities could gain the same user rights as the current user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights."
ZDI said the issue exists within the handling of CMarkup objects, and clarified that it had notified Microsoft on May 8 of its intention to publish details of the exploit.