Thanks again.
I would say that the most interesting part here is going through how Bitcoin was used in the darknet and how they laundered their money through bitcoin. Also, since Bitcoin was a global phenomenon the rise of illegal stuff sold on the internet went international as well. We can't deny that Bitcoin gain popularity because of the darknet, but it has been transitioning to a more mainstream usage like online payment for services and licit products online.
If you're a finance, business or similar majors, then discussing money laundering through bitcoin might be a good approach. Then if it's about security, you could go and discuss how money transactions can be more secure using bitcoins.