Know your enemies. That old proverb is sound advice for the Internet. Know what the bad guys want and how they go about getting it. If you keep that in mind, you can protect yourself. Your new enemies come in many forms, both human and otherwise:
Malware, or “malicious software,” which includes viruses, snooping programs, and programs that open “back doors.”
Hackers— how they find you, how they get in, and what they do once they're there.
Spammers— maybe they're criminals, maybe not. They're certainly an unacceptable threat to your privacy.
Hoaxes— These run the gamut from amusing to annoying to dangerous. Best not to take chances.