They say things like "There is a problem with this Web site's security certificate." If you're like most people, you may feel vaguely uneasy, and -- according to a new paper from researchers at Carnegie Mellon University -- there's a good chance you'll ignore the warning and click through anyway.

In a laboratory experiment, researchers found that between 55 percent and 100 percent of participants ignored certificate security warnings, depending on which browser they were using (different browsers use different language to warn their users).

"Everyone knew that there was a problem with these warnings," said Joshua Sunshine, a Carnegie Mellon graduate student and one of the paper's co-authors. "Our study showed dramatically how big the problem was."

That's not great news. Often the warnings pop up because of a technical problem on the Web site, but they can also mean that the Web surfer is being redirected somehow to a fake Web site. URLs for secure Web sites begin with "https."

The researchers first conducted an online survey of more than 400 Web surfers, to learn what they thought about certificate warnings. They then brought 100 people into a lab and studied how they surf the Web.