Crackproof Your Software: Protect Your Software Against Crackers (With CD-ROM)
"...an excellent read."  --LinuxLookup"A must-read for shareware programmers who want to protect their work. Comprehensive and well-written coverage of the topic." --About.com, February 2004"You can hold off the crackers a good long time with the ideas in ... [this] book by No Starch Press." --Gerard Beekmans, DevChannel.org