As in previous, large-scale attacks based on legitimate Web sites, this one involves hackers who execute SQL injection attacks to first compromise the site. In a SQL injection attack, hackers exploit vulnerabilities in Web applications that rely on a back-end database, which then gives them a way to add and run malicious code, usually rogue JavaScript, against any browser.

Microsoft acknowledged that attacks have become a significant problem. "Based on our stats, since the vulnerability has gone public, roughly 0.2% of users worldwide may have been exposed to websites containing exploits of this latest vulnerability," Mador and Saadecom said. "That percentage may seem low, however it still means that a significant number of users have been affected."

The move to legitimate, but hacked, sites is a change in tactics. As recently as Thursday, attacks were coming only from malicious sites, most of them in China. Even then, however, Microsoft had warned that hackers would probably expand the scope of their attacks by compromising valid sites.

In related news, Microsoft said it was working on a patch for IE, although it has still not said when it would issue the update. Some researchers expect the company to release a fix outside Microsoft's normal monthly schedule; the next security updates aren't due until Jan. 9, 2009. Microsoft also revised its Saturday, adding more information about the users should take until a patch is available. The company has offered up a total of nine different workarounds for IE users, several of which require editing of the Windows registry, a chore most users assiduously avoid.