The Dark Side of the Web -- Internet Malware

If I've been the target of a phishing scam I wasn't aware of the fact. I never open emails or attachments from people, places, companies, etc that I don't know. Just the other day I received an email from a family member warning about the latest internet virus; having something to do with an Obama speech that comes with an attachment. A friend and I started talking about how we didn't understand why people open emails and documents in which the sender is unknown to them. But I guess people do this often enough. I'm just super-paranoid and would assume receiving something from an unknown sender would be a huge, red flag to the person that it is a scam or virus of some sort and to not open it.