The Ten Most Dangerous Things Users Do Online, Be Careful

1. Clicking on email attachments from unknown senders
2. Installing unauthorized applications
3. Turning off or disabling automated security tools
4. Opening HTML or plain-text messages from unknown senders
5. Surfing gambling, porn, or other legally-risky Websites
6. Giving out passwords, tokens, or smart cards
7. Page 8: Random surfing of unknown, untrusted Websites
8. Attaching to an unknown, untrustworthy WiFi network
9. Filling out Web scripts, forms, or registration pages
10. Participating in chat rooms or social networking sites


Source : Bleepingcomputers