First off I think the most serious one is collecting information about children because even if it wasn’t illegal its very weird and most people who do that probably aren’t doing that for good reasons. The second one I would say would be sharing passwords and addresses online and I say that because I would imagine people would do that out of spite so it could happen frequently. The third one that I would say would be faking your identity because it could potentially harm others. The fourth would be using other people’s internet networks because most of the time this does negatively effect others due to the person wanting to do or purchase bad things but not wanting to be traced back to them. The fifth one that I would say would be bullying and trolling just because its hard to know what people are going through in real life so it can be super dangerous to push someone over the edge.