(IDG) -- Microsoft might want to consider putting Bulgarian programmer Georgi Guninski on the payroll. The software maker has acknowledged that Guninski discovered yet a third security flaw in Internet Explorer 5 browser software.

The latest flaw, under certain circumstances, would let a Web site access and read contents of files and folders on the computers of users, Microsoft says in a security bulletin posted online. The Web site operator would have to know the name of the file and the folder in which it was located in order to access it, and would not be able to list folder contents or create, modify or delete files, according to Microsoft.

The company is working on a patch for the flaw, but in the meantime is suggesting that users disable active scripting in the Internet zone. This is an IE security zone in which all Internet Web sites are automatically categorized.

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IE 5 restricts the actions that a Web site can take on computers of visitors.

"When software on the Web server requests that particular action be taken on a visiting computer, IE examines it and only allows the request to be made if it's appropriate. However, not all of the checks are present if the requesting software lies within an IFRAME. Specifically, certain requests that are made via a scripting method called ExecCommand are not properly bounded if invoked on an IFRAME," according to a question-and-answer section about the latest flaw posted on Microsoft's Web site.

An IFRAME is a sub window within the main browser window, and is viewed by the software running in it as its own window, working separately from the main window, Microsoft says.

To disable active scripting in the Internet zone, users should:

While in IE 5, select "tools," then "Internet options." Click on the "security" tab.

Go to the box labeled "select a Web content zone to specify its current security settings" and click on "Internet" and then "custom level."

Scroll down to "scripting," which is a major heading and then locate the minor heading called "active scripting." Click the "disabled" button under "active scripting."

Click twice on "OK" to accept the changes.

Users also are being encouraged by Microsoft to add Web sites to the security zone called the Trusted Zone, containing sites that users trust will not take malicious action against user computers.

Additional information about the flaw can be found at http://www.microsoft.com/security/bulletins/MS99-042faq.asp or at http://www.microsoft.com/security/default.asp.

The security bulletin from Microsoft acknowledges Guninski's role in bringing the problem to light. Last month, he was credited for finding a second security flaw in IE 5. That flaw could let a malicious Web site operator read files on user computers or on other computers in the user's local intranet. The flaw was found in the "download behavior" feature of IE 5.

A Microsoft spokesman could not be reached to comment about the latest flaw or to provide information about whether any Web users appear to have used the bug to access data on users' computers.

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Additional information about the new flaw
Microsoft Security Advisor

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