A hacker has posted attack code that could be used to break into PCs running older versions of Microsoft's Internet Explorer browser.
The code was posted to the Bugtraq mailing list by an unidentified hacker. According to security vendor Symantec, the code does not always work properly, but it could be used to install unauthorised software on a victim's computer.
"Symantec has conducted further tests and confirmed that it affects Internet Explorer versions 6 and 7," the company wrote on its website on Saturday. "We expect that a fully-functional reliable exploit will be available in the near future."
Security consultancy Vupen Security has also confirmed that the attack works, saying it worked on a Windows XP Service Pack 3 system running IE 6 or IE7. Neither company was able to confirm that the attack worked on Microsoft's latest browser, IE8.
Symantec did not report that the attack is being used by cyber-criminals, but because Internet Explorer is so popular, this type of code is highly coveted by hackers. If the software does pop up in online attacks, it will put pressure on Microsoft to rush out an emergency patch, ahead of its regularly scheduled December 8 security update. Microsoft could not be reached Saturday for a comment on the issue.
Together, IE 6 and IE 7 command close to 40 percent of the browser market.