New versions of the Mozilla Foundation's browsers have reintroduced a 7-year-old flaw that makes them vulnerable to spoofing attacks, security advisory company Secunia said yesterday.

Secunia first publicized the flaw last summer, warning that a feature built into most browsers for years was a security liability. The firm argued that a feature allowing one Web page to load arbitrary content into a frame of another page could allow an attacker to, for example, substitute his own log-in window on a bank's Web site. The feature was found in Internet Explorer, Mozilla, Opera, Safari and Mozilla derivatives such as Konqueror.

"We believe that it is important that Microsoft and the other vendors seriously consider the minor gains from such 'functionality' against the possible consequences for their customers," said Secunia Chief Technology Officer Thomas Kristensen last summer at the time of the flaw. "In our opinion, this is a vulnerability and should be treated as such, whether the vendors implemented this intentionally or not."

The Mozilla Project said it is investigating the report, and a moderator of the organization's online support site said the flaw had not been exploited. "To protect yourself, close all other windows/tabs before accessing a site where you routinely put in a secure password (your bank or PayPal account), or your bank or credit card details (e.g., Amazon), or other sensitive data," the moderator said.