By its very nature, an ordinary email message is as insecure as a postcard. It takes only the most rudimentary technical knowledge to "spoof" a message so that it appears to be coming from someone other than the actual sender. In fact, a favorite hacker trick is to send bogus mail messages that appear to have come from famous individuals such as Bill Gates. And because email travels in packets across the Internet, it's theoretically possible for anyone to intercept a transmission, read a message sent to someone else, and change the contents of that message.