Another security problem has cropped up to plague Microsoft's browser software.

The software giant has admitted a vulnerability in its Internet Explorer 5, that could allow a malicious Web site operator to read the files on the computer of a person who goes to the site, or on other computers on that user's local intranet.

Microsoft said it is working to develop a patch to fix the problem. Meanwhile, it is advising users to protect themselves by disabling the Active Scripting feature in IE 5.

Microsoft posted a warning on its Web site saying it had discovered the flaw in an IE 5 feature called "download behavior", intended to allow Web page authors to download files of client-side script, which is software designed to be run by the browser. Such software is designed to allow the Web site to download files that are in its domain only, and thus prevents the users' files from being accessed.

However, an ill-intentioned Web site operator could bypass domain restrictions, and use download behavior to gain read access to files on the user's machine or local intranet, according to the Microsoft Web site.

A malicious Web operator would have to know specific file names to read them and could not copy, delete or alter them, said Scott Culp, a Microsoft security product manager. He added that there have been no reported security breaches.

The problem was reported by Georgi Guninski, a Bulgarian programmer who earlier found another Microsoft security flaw, Culp said.

The vulnerability can be stopped by disabling Active Scripting following these steps:

  • In IE, select the Tools, then Internet Options, then click on the Security tab.
  • Select the Internet Zone, then click on the "Custom Level" button.
  • Under "Scripting," find the entry labeled "Active Scripting" and set it to "Disable."
  • Click OK twice to return to IE.

Microsoft said it will deliver a patch for a safe, new version of Download Behavior, which will be available at http://www.microsoft.com/security/.

Microsoft has been hit by numerous security flaws in recent months. Last week, the company released a patch for Internet Explorer that eliminated the "ImportExportFavorites" vulnerability, a hole that allowed a Web site operator to carry out any function that visitors to a Web site could do on their own computers.