Firstly, I dont think this guy is sinister. I dont see the need to jump to conclusions. Many modern laptops have built in wifi devices, so no need for a dongle. There are a number of explanations. But it does bring up the point of security. Most people have unlimited broadband, so it wont cost you extra if someone is using your wifi. The main risk is security, and also if the person downloads illegal material. If the downloads are traced back to your wifi, it could mean serious criminal issues. Always use a secure password. Its commonsense.