While the AS400 is not directly affected by viruses, the integrated file system may harbor an infected Microsoft document. We use the AS400 as our main server and document storage device. All the desktops connect to it when they boot. When I was looking for a network anti-virus solution, I decided on Sophos because it is AS400 compatible. The Win9x central installation directory resides on the AS400 as a shared folder. I update it with new virus definitions every few weeks and all of our desktops automatically update themselves from the central directory. It's a snap keeping all of our machines current.