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Using Internet Explorer hasn’t gotten any safer in the past few days as a Dutch security hacker, Jelmer Kuperus, pointed out yet another unblocked security problem in the popular Web browser.

The latest exploit, an attack on a Windows ActiveX component called Shell.Application, is similar to the Download.Ject attack, also called JS.Scob.Trojan. In that exploit, crackers broke into IIS servers on several popular but still unnamed sites and used them to spread keyboard loggers, proxy servers and other malware through IE’s ActiveX scripting technology.

Indeed, attackers used the spyware technique of installing a pop-up ad program, except this one silently installed a Trojan and a BHO (Browser Help Object) designed to swipe login information from several dozen financial sites.

Click here for more on the pop-up program.

The sites that spread the malware have since been fixed, but there has been no master shipping solution for the underlying IE vulnerabilities. Disabling Active scripting and ActiveX controls in the Internet Zone and Local Machine Zone will prevent exploitation of these holes, but at the cost of seriously affecting IE’s functionality.

Microsoft shipped a “patch” Friday that addressed part of this security problem by disabling the Windows component called ADODB.Stream.

For insights on security coverage around the Web, check out Security Center Editor Larry Seltzer’s Weblog.

Because of these developments, CERT (the U.S. Computer Emergency Readiness Team) and some IT professionals are recommending that users consider using other browsers such as Opera, Mozilla and Firefox.

Others, noting how so much business depends on ActiveX-powered Web sites, are sticking with Internet Explorer in the hopes that forthcoming Microsoft IE security patches and Windows XP SP2 (Service Pack 2) will protect their systems from the newly exploited IE security holes.

But many enterprises are reluctant to dump IE because they run so many IE-specific intranet applications. Click here to read more.

XP SP2 is expected to stop such attacks by hardening the barriers between processes running on the Internet Zone and on the far more dangerous Local Machine Zone, according to Thor Larholm, senior security researcher at PivX Solutions LLC, a security firm based in Newport Beach, Calif.

But in the meantime, Kuperus has published code that he claims can be used to break into Windows systems running IE with the Shell.Application exploit. The possibility of attacks using Shell.Application has been known in security circles since at least January 2004, when it was reported in the @RISK newsletter from The SANS Institute, a cooperative security research and education organization.

The Shell.Application exploit, like Download.Ject before it, makes it possible for crackers to create malicious, self-executing HTML files that can install and run an executable on the Web browser’s PC.

At this time, however, there have been no reported attacks using the Shell.Application exploit. Microsoft is working on security updates for Internet Explorer that will address this and other ActiveX security problems.

Larry Seltzer contributed to this story.

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