There are many layers of security from physical security to ensure that computers do not walk out the door, to firewalls that protect the business against outside attack over the Internet. Some security measures are easy to implement, others may be more complex and take some thought as to how tight to make the security vs. the needs of the users for systems to be usable and easy to access.
According to Gartner Group, Eighty percent of [security] failures are the direct result of mis-administration and poor configuration.