You can learn a lot by hacking into your own system. If you can gain access to your systems from a workstation outside your network, you can easily test your packet-filtering scheme without any outside exposure. If you do spot a weakness, you'll be one step ahead of the hackers. When in doubt, ask a consultant. If you don't have the technical wherewithal in-house or if your staff is too busy working on other projects, don't hesitate to call in a consultant.
Many companies offer security assessment and training services.
To make matters worse, network intrusion programs that automatically scan networks and query corporate DNS servers looking for holes are becoming increasingly available to hackers, who use these programs to test a system's locks the way a traditional burglar might jiggle a doorknob. Thankfully, all it takes is a bit of housekeeping to reduce your chances of becoming a victim. First, if yours is one of the many companies that runs outdated DNS software, an upgrade is definitely in order. Install the latest version of your DNS software immediately. Although services and file sharing capabilities are available on both Windows and Unix, Windows computers receive the brunt of file sharing attacks from Trojan horses and share compromises.