One thing I have enjoyed studying most in my research is the spread of malicious data (be it a program or a piece of intentional misinformation) through a network. One practical reason for this fascination is that it plays a key role in both offensive and defensive security. Offensively, understanding the key nodes in a network allow you to figure out a path inside a network. As a defender, you can use it as another tool to help decide where to allocate your all-to-limited resources for maximum effect.
