Highly Recommended Book

To anyone interested in computer viruses, their origins, and their functioning with an involved or better knowledge of computers, I would highly recommend legendary virus analyst Peter Szor's The Art of Computer Virus Research and Defense. You can find it at Amazon.com for a scant $32.99, which is very much worth this in-depth, 744 page book. From the cover:

Symantec's chief antivirus researcher has written the definitive guide to contemporary virus threats, defense techniques, and analysis tools. Unlike most books on computer viruses, The Art of Computer Virus Research and Defense is a reference written strictly for white hats: IT and security professionals responsible for protecting their organizations against malware. Peter Szor systematically covers everything you need to know, including virus behavior and classification, protection strategies, antivirus and worm-blocking techniques, and much more.

Szor presents the state-of-the-art in both malware and protection, providing the full technical detail that professionals need to handle increasingly complex attacks. Along the way, he provides extensive information on code metamorphism and other emerging techniques, so you can anticipate and prepare for future threats.

Szor also offers the most thorough and practical primer on virus analysis ever published—addressing everything from creating your own personal laboratory to automating the analysis process.