"Internet Security - Weaknesses and Targets" gives a detailed introduction on problems concerning Internet and Intranet security. After starting with some remarks on risk analysis and computer crimes, security weaknesses and targets are discussed in detail. Besides, more introductions are provided on: human factor and technical failures, attacks on accounts and passwords, attacks on Internet protocol, misuse of design and programming errors, weaknesses in common operating systems, targets in the WWW, and viruses. The lecture concludes with the discussion on possibilities to detect attacks and intrusions and ethical issuses are introduced as well.