Securing LAN
One way to secure your LAN connection is to use a separate network for your LAN. If you use a TCP/IP protocol for any of your network adapters you are connected to the internet and are open to unwanted visitors. It is simple to prevent this threat of becoming an easy attack point for hackers. Open the TCP/IP properties and uncheck the Client for Microsoft Networks and the File and Printer Sharing, also uncheck the Microsoft Family Logon.
Other way your LAN can be attacked is from the inside. It can be as simple as an attacker gaining access to the wiring closet. It is very important to make sure that your wiring closet is secure using some type of ID access, being ID card, Finger Print, or combination code. For the best method I would recommend using a at least two of these access methods.

Securing WAN
One threat to your VAN is eavesdropping; this is where a hacker uses software to intercept the data being via the WAN. To prevent this from being a problem for your company you want to use an encryption and VPN tunnels for end-to-end secure IP communications. The administrator should create a data classification standard and the policies, procedures, and guidelines should always be followed.
Another way to protect your WAN is to apply filters to your exterior IP stateful firewalls and IP router WAN interfaces to block TCP SYN and ICMP. The network administrator should contact the ISP to put the proper filters on its IP router WAN interfaces in accordance with CERT Advisory CA-1996-21.