changing shell from zsh to bash

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http://askubuntu.com – My web server was tampered by someone who was using zsh shell. I feel more comfortable using bash shell, as that's the defaults that come with Ubuntu and OS X (the two main operating systems I use). But this questions is focused on Ubuntu server. I have 4 websites running on this web server, I use byobu, I use tmux, I use ruby/ruby on rails, node.js, apache, a few daemons. If I switch the current root shell from zsh to bash, could there be any negative side effects that might result from this switch? For example, will processes be killed because their parent process (the shell) has been switch (HowTos)