how to prevent fork bomb

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To prevent fork bomb I followed this http://www.linuxhowtos.org/Tips%20and%20Tricks/ulimit.htm
ulimit -a reflects the new settings but when I run (as root in bash) :(){ :|:&};: the VM still goes on max CPU+RAM and system will freeze.
How to ensure users will not be bring down the system by using fork bombs or running a buggy application?
OS: RHEL 6.4


down vote
To make this change pervasive you'll need to add these limits to the entire environment. Changes using the ulimit command are only to the current environment.
NOTE: This will have no effect on the root user!

Example

Edit this file: vi /etc/security/limits.conf and add entries to the file limiting the number of processes (nproc) that a specific user or group of users' is allowed to have.
vivek hard nproc 300
@student hard nproc 50
@faculty soft nproc 100
@pusers hard nproc 200

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