Microsoft has acknowledged that a flaw in Internet Explorer could hit more recent versions of the browser, including those shipping with new operating system Windows 7.
Microsoft was quick to stress that it had not seen "successful attacks" against IE7 or IE8, but explained that researchers had developed "proof of concept" attacks against the browser.
The flaw is thought to be the one used by Chinese hackers to attack Google and other net firms, leading to a standoff between the country and search engine.
Senior security communications manager Jerry Bryant wrote on the Microsoft security blog that the "attacks remain targeted to a very limited number of corporations and are only effective against Internet Explorer 6."
He stressed that Microsoft has "not seen successful attacks" on IE7 or IE8, although researchers have found a way to target the former.
"However, earlier today, we were made aware of reports that researchers have developed Proof-of-Concept (PoC) code that exploits this vulnerability on Internet Explorer 7 on Windows XP and Windows Vista," he noted. "We are actively investigating, but cannot confirm, these claims."
Microsoft has advised its users to upgrade to IE8, and said a patch will be released soon.
"We want to let customers know that we will release this security update as soon as the appropriate amount of testing has been completed," he said. "While we cannot yet give a date of when that will be we will keep customers updated."
The governments of Germany and France have both advised against using Internet Explorer, but the UK government is sticking with Microsoft.
Speaking to the Guardian newspaper, a Cabinet Office spokesperson said: "it doesn't think the issue [of being open to hacking] would be resolved any better by going elsewhere".
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