PBS.org spokesman Kevin Dando declined to provide much detail, but he says PBS became aware of the introduction of a rogue authentication screen on the Web site and took steps to eliminate it and fix the Web site. According to Purewire, which noticed the problem and reported it to PBS.org, the rogue authentication screen on PBS.org worked by trying to break into a visitor's desktop computer by exploiting a variety of and other applications that might be on the victim's desktop.

"There was possibly a vulnerability in the site," Dando says. "This week the concentration has been on fixing it."

PBS.org was alerted both through its own internal systems and from Purewire about the matter, Dando says, adding PBS had received no e-mail input from site visitors about the rogue authentication screen, which may mean that few visitors came in touch with it.