Linux Militia has a CTF team forming
CTF Time – Competitive CTF (Team) (message for invite)
CTF Linux Militia team
CTF Learn – Individual challenges and learning portal
Join our team and join our Discord server! (Send message for login approval).
“In computer security, Capture the Flag (CTF) is a computer security competition. CTF contests are usually designed to serve as an educational exercise to give participants experience in securing a machine, as well as conducting and reacting to the sort of attacks found in the real world. Reverse-engineering, network sniffing, protocol analysis, system administration, programming, and cryptanalysis are all skills which have been required by prior CTF contests at DEF CON. There are two main styles of capture the flag competitions: attack/defense and jeopardy.
In an attack/defense style competition, each team is given a machine (or a small network) to defend on an isolated network. Teams are scored on both their success in defending their assigned machine and on their success in attacking the other team’s machines. Depending on the nature of the particular CTF game, teams may either be attempting to take an opponent’s flag from their machine or teams may be attempting to plant their own flag on their opponent’s machine. Two of the more prominent attack/defense CTF’s are held every year at DEF CON, the largest hacker conference, and the NYU-CSAW (Cyber Security Awareness Week), the largest student cyber-security contest. 
Jeopardy-style competitions usually involve multiple categories of problems, each of which contains a variety of questions of different point values and difficulties. Teams attempt to earn the most points in the competition’s time frame (for example 24 hours), but do not directly attack each other. Rather than a race, this style of game play encourages taking time to approach challenges and prioritizes quantity of correct submissions over the timing.”