How is computer information protected?

It heavily depends on software installed on them.

For example, computers with Windows installed aren't very secure, unless they have a firewall and antivirus installed.

Linux is secure, unless somebody configures it to not be secure.

Linux

BSD is security-oriented, so it's very secure.

As for hardware - not very much, since one can take out a hard disk and read it elsewhere, boot a LiveCD/DVD and crack local passWord, etc.