(Free) Virtual Networks (VPNs)
===

* ChaosVPN: http://wiki.hamburg.ccc.de/ChaosVPN
* Gh0st Networks: http://www.gh0st.net/
* Hacking Lab: https://www.hacking-lab.com/
* p0wnlabs: http://p0wnlabs.com/
* pwn0: https://pwn0.com/
* PentestIT: https://lab.pentestit.ru/

Custom Personal Targets
===

* Hack A Server: https://hackaserver.com/
* Hack Me: http://hack.me/
* Hack This: https://www.hackthis.co.uk/levels/
* Smash The Stack: http://smashthestack.org/
* Hack The Box: https://www.hackthebox.gr/
* SecAdvise: https://labs.secadvise.com/
* DarkHive: http://darkhive.net/
* Avatao: https://avatao.com/
* Root-Me: https://www.root-me.org/

Archive/Repository
===

* Security Conference Library: http://archive.liquidmatrix.org/
* Shell-Storm.org Repository: http://repo.shell-storm.org/CTF/

Books
===

* Assembly Language Step-by-Step: Programming with Linux [ISBN-13: 978-047-04-9702-9]: http://www.amazon.com/Assembly-Language-Step-Step-Programming/dp/0470497025/
* Brute Force Vulnerability Discovery [ISBN-13: 978-032-1-44611-4]: http://www.amazon.com/Fuzzing-Brute-Force-Vulnerability-Discovery/dp/0321446119/
* Bug Hunter's Diary [ISBN-13: 978-1-59327-385-9]: http://nostarch.com/bughunter
* Hacking: The Art of Exploitation [ISBN-13: 978-159-327-144-2]: http://www.amazon.co.uk/Hacking-Art-Exploitation-Book-Package/dp/1593271441/
* Metasploit: The Penetration Tester's Guide [ISBN-13: 978-159-3-27288-3]: http://www.amazon.com/Metasploit-Penetration-Testers-David-Kennedy/dp/159327288X/
* Operating Systems Design and Implementation (3rd Edition) [ISBN-13: 978-013-142-938-3]: http://www.amazon.com/Operating-Systems-Design-Implementation-Edition/dp/0131429388/
* The Art of Exploitation (2nd Edition) [ISBN-13: 978-1-59327-144-2]: http://www.amazon.com/Hacking-Art-Exploitation-Jon-Erickson/dp/1593271441/
* The Shellcoder's Handbook [ISBN-13: 978-0-76454-468-2]: http://www.amazon.com/The-Shellcoders-Handbook-Discovering-Exploiting/dp/0764544683/
* The Web Application Hacker's Handbook (2nd Edition) [ISBN-13: 978-1-11802-647-2]: http://www.amazon.com/Web-Application-Hackers-Handbook-Exploiting/dp/1118026470/

Misc
===

* Bug crowd: http://bugcrowd.com/
* CTF Time: http://ctftime.org/
* CTF365: http://ctf365.com/
* Hacker Cons: http://hackercons.org
* Hat Force: https://www.hatforce.com/
* Intense School: http://www.intenseschool.com/resources/
* SECore: https://secore.info/
* We Chall: https://www.wechall.net/
* WirelessPentest: https://web.archive.org/web/20140802203941/http://www.wirelesspentest.com/

Programming
===

* Codec Ademy: http://www.codecademy.com/
* Learn {Python,Ruby,C,Regex,SQL,CLI} The Hard Way: http://learnpythonthehardway.org/book/
* Learn {Python,Java,C,JavaScript,PHP,Shell,C#}: http://learn-c.org/
* PHP - The Right Way.: http://www.phptherightway.com/
* Rails for Zombies: http://railsforzombies.org/

Security Courses
===

* ComputerSecurityStudent: https://www.computersecuritystudent.com/
* eLearn Security: http://www.elearnsecurity.com/
* Hacking Dojo: http://hackingdojo.com/
* MDSec: http://mdsec.net/
* Offensive Security: https://www.offensive-security.com/
* Security Tube Training: http://www.securitytube-training.com/
* The Hacker Academy: http://www.thehackeracademy.com/

Training Material
===

* nets.ec (used to be called "Blackhat Library"): https://nets.ec/Main_Page
* Codecademy: http://www.codecademy.com/
* Corelan: https://www.corelan.be/index.php/articles/
* End Game (How to Get Started in CTF): http://www.endgame.com/
* Hacking Cisco: http://hackingcisco.blogspot.com/
* Metasploit Unleashed: http://www.offensive-security.com/metasploit-unleashed/
* N00b pentesting: https://web.archive.org/web/20120412031808/http://n00bpentesting.com/lessons
* Open Security Training: http://opensecuritytraining.info/
* Pentest Standard: http://www.pentest-standard.org/index.php/Main_Page
* Router Gods: http://www.routergods.com/
* SWEET (Secure WEb dEvelopment Teaching): http://www.csis.pace.edu/~lchen/sweet/
* SEED: Vulnerability and Attack Labs: http://www.cis.syr.edu/~wedu/seed/all_labs.html
* Security Tube: http://www.securitytube.net/