How hackers, viruses, and worms attack computers from the Internet and exploit security holes in software is explained in this outline of antivirus software, patches, and firewalls that try in vain to withstand the storm of attacks. Some software's effectiveness exists only in the imaginations of its developers because they prove unable to prevent the propagation of worms, but this guide examines where security holes come from, how to discover them, how to protect systems (both Windows and Unix), and how to do away with security holes altogether. Unpublished advanced exploits and techniques in both C and Assembly languages are included.