Researchers warn that IE attacks are increasingly being launched from legitimate Web sites; Microsoft says it is working on a patch

Microsoft warned Saturday of a "huge increase" in attacks exploiting a critical unpatched vulnerability in Internet Explorer (IE), and said some originated from hacked pornography sites.

Other researchers confirmed that attacks were increasingly coming from compromised Web sites.

Microsoft noted the upswing in attacks on the company's Malware Protection Center blog late Saturday. "The trend for now is going upwards," said researchers Ziv Mador and Tareq Saadecom on the blog. "We saw a huge increase in the number of reports today compared to yesterday."

Hackers have been exploiting a data binding bug in IE for more than a week, according to researchers who first noted in-the-wild attack code on Chinese servers. The vulnerability, which exists in all versions of the Microsoft browser, including IE5.01, IE6, IE7, and IE8 Beta 2, has so far been exploited only by attack code that targets IE7, the most widely used edition.

Mador and Saadecom said that attacks are increasingly being launched from legitimate Web sites. "Some legitimate Web sites were maliciously modified to include the exploits," the two said. A popular Taiwanese search engine and a Hong Kong-based pornography site were among the sites hacked, then set up to attack visitors running IE.

Researchers at Trend Micro also reported a big increase in hacked sites serving exploits aimed at the new IE bug. On Saturday, the security firm estimated that about 6,000 sites have been infected so far, noting that the count was "quickly increasing in number."

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 percent of users worldwide may have been exposed to Web sites ontaining 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 security advisory for a third time Saturday, adding more information about the recommended actions 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.