There may be more ways, but Five Ways to Screw Up Your Life with the Internet covers some important ones:
One of the odd things about the Internet is that so many people don’t seem to understand that it’s real. Sure, they realize that there’s a computer in front of them, a “series of tubes,” and then…it gets kind of foggy. It’s like they think there are magical pixies from the land of Lulz on the other end, as opposed to their family, friends, co-workers, and old boyfriends who are obsessively poring over their Facebook page.
Granted, they are aware that they do need to be careful about a few things: viruses, hackers, identity thieves, Nigerian princes who want to give them millions of dollars — all the standard stuff. But there are some lesser known dangers of the Internet that can steamroll your life like Paris Hilton stampeding towards a line of cocaine.
See the five at the link.