Hey guys! I just wanted to introduce you to Metasploitable- An intentionally vulnerable Linux OS! (Somewhat similar to Nebula- what @L3akM3-0day had posted about). Now this OS was made to run from a VM, although if I'm correct you can also boot from a USB.
Here's the download: https://sourceforge.net/projects/metasploitable/
There is Metasploitable 2 available both are great to start hacking. I've done a tutorial on how to get a root shell on Metasploit 2. Great VM to learn a little bit of metasploit
Indeed it is!