Thank you for your feedback on this issue. The Confluence team have been carefully considering implementing this. After our analysis we have concluded that we will not be implementing any form of virus scanning capability within the product.
Confluence does have an extensive plugin framework where by we enable customers and partners to build plugins for this type of functionality on top of Confluence. We encourage customers who believe virus scanning of attachments is critical to their business process to reach out to one of our partners for assistance with custom plugin development.