Damn Vulnerable Linux (DVL) is a Linux-based (modified Damn Small Linux) tool for IT-Security & IT-Anti-Security and Attack & Defense. It was initiated for training tasks during university lessons.
DVL is full of vulnerable and exploitable software. NEVER use this system in any production environment!
Actually, it is a perverted Linux distribution made to be as insecure as possible. It is collection of IT-Security and IT-Anti-Security tools. Additional it includes a fullscaled lesson based environment for Attack & Defense on/for IT systems for self-study or teaching activities during university lectures. It's a Live Linux Distro, which means it runs from a bootable CD in memory without changing the native operating system of the host computer. As well it can be run within virtual machine environments, such as qemu or vmware. There is no need to install a virtual machine if you use the embedded option.
Damn Vulnerable Linux is highly integrated into the community project crackmes.de (http://www.crackmes.de) and is frequently updated with new community provided lessons.