Damn Vulnerable Linux is a security distro, which can be an excellent learning tool. The distro includes older version of popular software like Apache web server, MySQL, PHP and others. The objective to create such a distro is to let users try out known hacks and vulnerabilities on these technologies and hone their skills.
The distro is explained as,
DVL is a live CD available as a 1,8 GB ISO. It contains older, easily breakable versions of Apache, MySQL, PHP, and FTP and SSH daemons, as well as several tools available to help you compile, debug, and break applications running on these services, including GCC, GDB, NASM, strace, ELF Shell, DDD, LDasm, LIDa, and more.
DVL is made by people with significant black hat backgrounds, incorporating the community of ReverseEngineering.net and Crackmes.de. It contains a huge amount of lessons, including lesson descriptions and solutions if the level has been solved by a community member at Crackmes.de.
Apparently the distro has been made vulnerable to attacks and can be used to teach thread hijacking, buffer overflow, SQL injection and other forms of exploits.
The distro is sized at 1.8 GB and is available as a zip file. Head over to the Damn Vulnerable Linux (DVL) page to read more and download the distro.