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You'll only be able to reach the user level. Wipe that and you're golden. If you want to make things even more secure, don't use sudo. Separate the Root and User, use secure passwords, install a software firewall as backup to a hardware firewall and don't allow direct access to a network with internet access at any point along the chain.
There's an old adage of how to make a Windows PC more secure. Unfortunately, even disconnecting it from the Internet couldn't keep viruses away.