The problem: A 2006 survey by the FBI and the Computer Security Institute, an industry group, found that corporate security breaches originate inside organizations about as often as outside. Larcenous employees earn extra spending money by peddling company secrets and customer data, and newly terminated workers may be tempted to gorge on corporate secrets before they walk out the door for the final time.

The solution: Keep sensitive customer information off intranet "common areas" - like promiscuously shared network drives - and behind access-control mechanisms that log every visit. Install an intrusion-detection system, like the open-source Snort software that sniffs your LAN for attack signatures inside the firewall. Seed databases with "honey tokens," false data entries that can be used to trace a theft back to the source.