Note site:

http://ctftime.org
http://www.vnsecurity.net/about-us/clgt-ctf-team/
https://www.thc.org/
bkitsec.wordpress.com/
CentOS :
http://www.server-world.info/en/note?os=CentOS_6&p=initial_conf&f=6
Ollydbg tutorial:
http://thelegendofrandom.com/blog/sample-page
... tiếp tục cập nhật