Can anyone give me some points on this? ===================== What technical and procedural steps can an enterprise take to protect computer systems from unauthorised access and malicious code?

In my opinion, your best option would be a good NAT router with a built in firewall.

http://searchsecurity.techtarget.com/featuredTopic/0,290042,sid14_gci860052,00.html You'll find some good advice at this site.

A good NAT router is a must. A good hardware fire wall is very nice to have. Corporate Anti virus software. E-mail policies in exchange to block executable files. Policies in effect to not allow users to install software. Lock down file sharing and access to one location. (file server) If your a mean and paranoid admin.. Enable auditing on all files/folders/clients. If your super paranoid... set the server up to page/text msg/call you if/when a unauthorized access attempt was made. I could go on for ever here.... (Should I start working for the goverment?)