General Server Security
The security mechanisms the server itself provides vary from server to server and from architecture to architecture. Whatever server you choose to run, you should understand security and spend the time to implement them. Especially if you're running under a multi-user architecture like UNIX, you can easily overlook an item that may cause a potential hole.
Note:
It's the general consensus that of all the platforms on which you can run a WWW server, the one that is least likely to cause you security problems is the Macintosh. The fact that the Macintosh doesn't provide the capability to log in from anywhere but the console reduces the risks involved with providing external access to its filesystem. This also makes it a bit more difficult to manage the archive's contents as a team, of course, but this issue can be worked around through the Macintosh's file-sharing mechanisms. You may wish to investigate this alternative to a UNIX server.