GreyMagic Software detailed nine security vulnerabilities in Internet Explorer (IE) 5.5 and 6.0. Previous versions are not vulnerable, while only two of the vulnerabilities affect IE6 with Service Pack 1, according to GreyMagic.
With all the vulnerabilities combined, an attacker could "easily steal private local documents, forge trusted Web sites, steal clipboard information, and even execute arbitrary programs," GreyMagic said. An attacker would have to lure a user to a specially-coded Web site to carry out an attack.
"It would be extremely simple to exploit these new vulnerabilities," said Lee Dagon, security services coordinator at GreyMagic. "The code used to exploit a client is very short and straightforward and exploitation is as easy as getting someone to go to a specific Web page."
Users can check what version of IE is installed by clicking "About Internet Explorer" in the "Help" pull-down menu of the browser.
GreyMagic informed Microsoft at the same time as it disclosed details of the vulnerabilities to the public. The Israeli company said that in the past "notifying Microsoft ahead of time and waiting for them to patch the reported issues proved non-productive".
Microsoft said it was "concerned" at the way GreyMagic reported the vulnerabilities. "Publishing this report may put computer users at risk - or at the very least could cause needless confusion and apprehension," the company said in a statement.
"Responsible security researchers" work with the maker of the product that is suspected to be vulnerable to "ensure that countermeasures are developed before the issue is made public and customers are needlessly put at risk", Microsoft said.
GreyMagic has not heard from Microsoft since it reported the vulnerabilities on Tuesday, said Dagon.
"We end up reading about their reactions in various news items," he said. "Our primary goal in releasing these advisories is to alert users to the risks they are exposed to and suggest workarounds for them to employ. The way we see it, that is the responsible thing to do."
Microsoft did not confirm the existence of the vulnerabilities, but said it was investigating the issues reported by GreyMagic just as it investigates all reports of security flaws in its products.
GreyMagic advises users to disable Active Scripting in IE until Microsoft issues a patch.