Developing a secure information system

Please answer the 2 questions below. Thank you

Post your personal viewpoint upon the following issues:

Your boss is asking each engineer from all departments to come up with the one or two sources of network threats and attacks you consider the most critical and why. He wants you to be able to fit your thoughts on an index card. He does not care if the same problem is addressed from several points of view or if you address a very specific "threat of the day" or one from the past that could come back. You are also asked to have an opinion about the potential risks of such threats and attacks.

With limited time and resources your manager wants everyone to suggest the structure of a network defense system to protect the computers and the network. Since this is an open discussion if your favorite idea has been discussed "to death" pick the next. These are pro-active steps. Consider at least two solutions and why one ranks high on your mind.