The field of web security, and computer security in general, is large and growing larger every day. Rather than attempting to list all of the many useful references, we'll note the ones we think especially appropriate. For a more extensive and up-to-date listing of references, we recommend that you pursue an online reference such as the CERIAS hotlist (cited below). Appendixes D through F of Practical Unix & Internet Security, although somewhat dated, still contain a great deal of highly useful material. The CERIAS hotlist has thousands of references to Internet-based sources of security information; the PUIS book has almost 50 pages of references to journals, organizations, books, papers, and other resources in the indicated appendixes.