Internet is not sure, but very friendly to storage and manipulate data. Customer confidence in internet software is based on the ability of the site to prevent damages and attacks. But secure software is complicated, and depends of several factors : good risk estimation, good code architecture, cyphering, good web server configuration, good coding to prevent most common attacks, good identification and rights allocation.Based in particular on OWASP Project, the book explores all these themes to help computer students and developers who want to integrate security into their applications.