Responding to mounting complaints from users about the vulnerability of its Outlook e-mail client, Microsoft is to deliver a security patch for two versions of the software.

The patch, which is for the Office 98 and 2000 clients, but not the free Outlook Express software, was released yesterday through Microsoft's Office Update web site,

A completed version is expected to be available next week (22 May).

Users installing the patch will lose some functionality in Outlook but a growing number of users are willing to make that sacrifice in return for a more secure product, according to a company spokesman.

Roger Thompson, director of malicious code at said he wondered whether the company had gone too far in the opposite direction.

"I'm just wondering if they have broken more functionality than they needed to. The anti-virus people would have been pleased to see them just disable the launching of any applications from within Outlook."