Consider installing a personal firewall on each
computer on the network.
If you have notebooks/lap-top computers that are used
in locations outside of the office, each one of those should have a personal
firewall. They will not be protected by your corporate firewall when they are
outside of the office. The same thing goes for stationary computers used
from home offices.
A personal firewall typically has different features
a regular firewall. One of the things a personal firewall can do
is to enforce policies about which applications are allowed to
communicate with the outside world. If someone manages to download a program
to your computer, that sends off information to the Internet, a personal
firewall may protect you while a regular firewall probably will not.