Last week, a pair of security researchers spread the news that a new class of vulnerabilities, called "clickjacking," puts users of every major browser at risk from possible attack.

Robert Hansen, founder and chief executive of SecTheory, and Jeremiah Grossman, chief technology officer at WhiteHat Security, spilled some beans last week after they gave a semi-closed presentation at OWASP AppSec 2008 in the US.

Maybe because of the catchy name, perhaps because it's actually serious stuff, clickjacking got some press. But that still leaves open the question: Just how spooky is it? Are we talking run-for-the-hills scary, or is this just another theoretical attack vector? And what should you do to protect yourself?

We have questions, as usual, and fewer straight answers than we'd like.

What is clickjacking?

Good question. Getting to an answer, though, is a little tough, since Hansen and Grossman are keeping virtually all details confidential, at least for now. Here's how Grossman put it to Computerworld last week:

"Think of any button on any Web site that you can get to appear between the browser walls," he said last Friday. "Wire transfers on banks, Digg buttons, CPC advertising banners, Netflix queue..., the list is virtually endless and these are relatively harmless examples. Next, consider that an attack can invisibly hover these buttons below the users' mouse, so that when they click on something they visually see, they actually are clicking on something the attacker wants them to."

In plain English, clickjacking lets hackers and scammers hide malicious stuff under the cover of the content on a legitimate site. You know what happens when a car-jacker takes a car? Well, click-jacking is like that, except that click is the car.

Is clickjacking new?

Nope. Not only is it similar to a cross-site request forgery -- a type of vulnerability and attack that has been known since the 1990s -- but Hansen acknowledged that clickjacking goes back several years.

Coincidentally or not, Mozilla last week patched a clickjacking vulnerability in Firefox that was, in turn, a variant of a similar flaw in Internet Explorer that Microsoft first patched in 2003, then patched again in 2004.

How would a clickjacking attack work?

We're not sure, again, because of the paucity of information. But Michal Zalewski, a renowned security researcher who now works for Google, offered up one example.

"A malicious page in domain A may create an IFRAME pointing to an application in domain B, to which the user is currently authenticated with cookies," Zalewski said in a Thursday message to a mailing list. "The top-level page may then cover portions of the IFRAME with other visual elements to seamlessly hide everything but a single UI button in domain B, such as 'delete all items,' 'click to add Bob as a friend,' etc. It may then provide [its] own, misleading UI that implies that the button serves a different purpose and is a part of site A, inviting the user to click it."

In other words, the hacker would dupe users into visiting a malicious page -- through the usual methods -- but then hide the nasty bits under what appears to be the real-deal content from a legitimate site.