Why is it a good idea to perform a penetration test from the inside?

You are running known exploits against your network to test for possible vulnerabilities. To test the strength of your virus software, you load a test network to mimic your production network. Your software successfully blocks some simple macro and encrypted viruses. You decide to really test the software by using virus code where the code rewrites itself entirely and the signatures change from child to child, but the functionality stays the same. What type of virus is this that you are testing?

An Employee is suspected of stealing proprietary information belonging to your company that he had no rights to possess. The information was stored on the Employees Computer that was protected with the NTFS Encrypted File System (EFS) and you had observed him copy the files to a floppy disk just before leaving work for the weekend. You detain the Employee before he leaves the building and recover the floppy disks and secure his computer. Will you be able to break the encryption so that you can verify that that the employee was in possession of the proprietary information?

You have been called in to help with an investigation of an alleged network intrusion. After questioning the members of the company IT department, you search through the server log files to find any trace of the intrusion. After that you decide to telnet into one of the company routers to see if there is any evidence to be found. While connected to the router, you see some unusual activity and believe that the attackers are currently connected to that router. You start up an ethereal session to begin capturing traffic on the router that could be used in the investigation. At what layer of the OSI model are you monitoring while watching traffic to and from the router?

Gary, a computer technician, is facing allegations of abusing children online by befriending them and sending them illicit adult images from his office computer. What type of investigation does this case require?