Most e-mail viruses require the recipient to open the message or infected attachments, but a defect in the software permits the trigger of viruses upon receipt of the e-mail.
Microsoft has stressed that the loophole does not affect corporate users, but it does have implications for those running Outlook in “internet-only mode” and home users.
Microsoft is currently developing a patch which will remove the flaw in its software and it intends to make this available on its web site in the near future.