Network security is an infinitely complex and dynamic subject, implementing these simple measures will go a long way to protecting your Organization's LAN.
2, Disable drives:Disable floppy drive access, USB ports and serial ports on networked computers.
3, Restrict Permissions: Windows 2000 and 2003 server allow you to set permissions so that users can't run downloaded 'exe' or other executable files.
4, Block Instant Messenger:IM and its cousins, ICQ and Yahoo Messenger, sends messages and attachments out to a server and then back to its clients. You lose control when this happens.
5, Password Protect Your BIOS:A BIOS without an administrator password is an invitation to mischief.
6, Run AV Software: Run anti-virus software on all your computers.
7, Build Your Defenses: Install a firewall or a proxy server.
8, Beware Of Attachments From Unknown, Untrusted Sources:Do not open attachments to email unless you trust the sender.
9, Monitor Your Ports:Install a port monitor to prevent your ports from being scanned.
10, Encrypt Wireless Access.
11, Keep Back Office Systems Off The Organization Network
12, Require passwords to be changed frequently
13, Use CTRL+ALT+DEL to logon
14, Keep your networking skills up to date.