Danish information security consulting firm Secunia is warning Microsoft Internet Explorer users of a vulnerability that could enable Internet fraudsters to create more-realistic and authentic-looking fake Web sites.

Secunia says it has found an "input validation" error in Internet Explorer. By exploiting this vulnerability, known as a URL-spoofing vulnerability, attackers can display any URL name they wish in the address and status bars of IE.

This flaw would make it appear to Internet users that they're visiting a banking Web site, for example, when that site is actually a front for fraudsters attempting to collect sensitive financial information.

Secunia says the vulnerability has been confirmed in Internet Explorer 6.0, though other versions may be affected as well.

Microsoft has taken issue with the way Secunia made information about the flaw public.

"Microsoft is concerned that this new report of a vulnerability in Internet Explorer was not disclosed responsibly, potentially putting computer users at risk. We continue to encourage responsible disclosure of vulnerabilities," the company said in a statement.

Microsoft said it's investigating the flaw and that it's not aware of any affected customers or hacking tools that are available to take advantage of the flaw. In its statement, Microsoft said it would consider issuing a patch if needed.

Secunia has a test on its Web site for users to see if they're vulnerable to the URL-spoofing flaw. It's available here.