"XSS vulnerabilities do present a serious risk. However, to date their real-world use has been limited," said Oliver Friedrichs, director of Symantec Security Response in an e-mail. "XSS vulnerabilities can result in the theft of session cookies, Web site login credentials, and exploitation of trust. XSS vulnerabilities are site-specific, and therefore their life cycle is limited; they become extinct once they're discovered and repaired by the Web site owners."

Joseph Pierini, director of enterprise services for the ScanAlert "Hacker Safe" program, maintains that XSS vulnerabilities can't be used to hack a server. He maintains that XSS vulnerabilities aren't material to a site's certification. "Cross-site scripting can't be used to hack a server," he said. "You may be able to do other things with it. You may be able to do things that affect the end-user or the client. But the customer data protected with the server, in the database, isn't going to be compromised by a cross-site scripting attack, not directly."

Pierini dismisses the suggestion that certifying a site as "Hacker Safe" when it remains vulnerable to XSS attacks could be confusing to consumers. He insists that the meaning of the certification is clear and notes that his company's scanning service reports the XSS flaws it finds to its clients.

"We definitely identify this [XSS] and we definitely bring this to our customers' attention," he said." And we provide our customers with the information. Our customers are allowed to make the decision where to put their resources. I personally want them to put their resources where they're needed most, in things that can affect the confidentiality, the integrity, or the availability of that system that we're certifying. Cross-site scripting can be used to do a variety of things, but it's all on the client side. And that's an area that we don't have control over."