The company said its Microsoft Outlook Email Security Update is now available for download free of charge from the Office Update Web site.
Microsoft said the update offers a significant security upgrade by blocking access to potentially unsafe file types that virus writers target. In addition, the company said the new patch sets higher default security settings than previous versions of the software.
Microsoft has long faced criticism from some quarters for its lax security features--concerns that came to a head following the "I Love You" attack, which raced across the globe by hijacking Outlook accounts.
Analysts noted that the virus took advantage of well-known exploits involving Visual Basic script files, which end in the extension ".vbs." Visual Basic is a high-level programming language developed by Microsoft that is graphically oriented.
Microsoft in the past has resisted issuing security patches for Outlook, saying that they would hurt ease of use and undermine compatibility with other products.