If I may quote haqking from another thread he posted in:
The minute you, as the user or the admin allows anyone unsupervised physical access to your machine, it is effectively compromised.System security is not a product
System security is not a state.
System security is a process and ongoing and the responsibility of the User/Admin.
It does not matter what measures are in place in terms of software, passwords,keyrings. All it takes is a live cd, and your data is instantly accessible.
The sudo command is primarily about restricting permissions to carry out various tasks and actions whilst running the system. It is not in itself a robust security measure against anyone other than the uninitiated user.
Security is in the hands of the user/owner at all times and how they choose to deal with that responsibility is what determines the integrity of the data held on the machine (s)