Microsoft Corp. on Friday warned users of Internet Explorer (IE) 5.5 and 6.0 that a vulnerability in the software could allow a hacker to gather information from a user's IE "cookies" by enticing them to view certain Web sites.
If users visited a site with a certain type of maliciously formed URL (Uniform Resource Locator), or viewed that site by opening an HTML e-mail message, a hacker could view or change information in the user's cookies, according to a Microsoft security bulletin.
Cookies are pieces of information that some Web sites store on a user's PC, usually to make it easier for frequent visitors to use that Web site. They sometimes contain sensitive information, such as a user's address or credit card number.
Users who receive e-mail on Microsoft Outlook Express can avoid being attacked through this vulnerability if they set Outlook Express to use the "Restricted Sites" Zone, which disables the Active Scripting feature. This is the default setting on Outlook Express 6.0.
The vulnerability may also exist on earlier versions of IE, but Microsoft has not verified whether it does. Older versions of the product are no longer supported, according to Friday's bulletin. The company didn't say how many users, if any, had been affected by the problem.
No patch for the vulnerability exists yet, because the person who discovered the issue made it public just days after informing Microsoft, the company said. Microsoft and a group of security companies said this week they want to require users who report a vulnerability to wait at least 30 days before making it public. The security bulletin can be found on the Web at http://www.microsoft.com/technet/.