Staying hidden on a network helps protect your privacy and increases your security since other MacBooks on your network can see your computer in the Shared section of the Finder. However, unless you allow access or someone discovers your credentials, those that can see your MacBook still won't have the ability to access your data. Even so, If you want the best security, you can modify your sharing settings to hide your presence and reduce or eliminate the chance of another user accessing your MacBook.
Mac OS X Mavericks provides several options to disable different types of sharing on your MacBook. By launching System Preferences and clicking on the "Sharing" option, you can access all of the currently active settings. If you want to completely disable all sharing options, uncheck all of the items in the list of services. This includes Screen Sharing, File Sharing, Printer Sharing, Internet Sharing and Bluetooth Sharing. Later on, if you need to share a file with another user, you can enable these options on a case-by-case basis. You should also disable the Remote Management, Remote Login and Remote Apple Events options.
For maximum security, you can go offline and eliminate the possibility of a third-party accessing your computer. This option provides one of the simplest methods of hiding your computer from others. When you disconnect your computer from the Internet, a person must gain physical access to your computer to view any data on the machine. If you only connect using an Ethernet cable, then your computer won't show up in the Shared section of another MacBook. Disconnect the cable from your MacBook's Ethernet port to disable access. If you connect with others using a FireWire or Thunderbolt cable, you must also disconnect those cables.
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Disable your Wi-Fi connection to prevent the possibility of accidentally connecting to a Wi-Fi network or to remove your MacBook from a currently active network. Turn off Wi-Fi access by opening System Preferences, clicking on "Network" and selecting the "Wi-Fi" option in the sidebar. Select the "Turn Off Wi-Fi" button and then check the "Show Wi-Fi Status in Menu Bar." Enabling the menu bar option gives you the ability to click the menu bar icon and turn Wi-Fi on or off. Bluetooth connections also provide a way for others to see your computer online. Click the "Turn Bluetooth Off" button in the Bluetooth section of System Preferences to disable broadcasting your MacBook.
If you disconnect any currently active computer-to-computer networks you won't benefit from the shared resources provided by those computers. Any networking settings you configured for computer-to-computer network get lost the moment you disable them. Sometimes called ad-hoc networks, these networks provide a convenient way to share files, folders, stream media and perform other functions. If your computer connects to the Internet using an Ethernet cable, and other computers on your ad-hoc network rely on that connection, then disabling your network also blocks them from accessing the Internet.
OS X comes with a built-in firewall that provides robust options to help keep you safe if you do decide to stay online. By default, the firewall is not enabled. To turn it on, access System Preferences and select the "Security & Privacy" option. Click the "Firewall" tab and select "Turn On Firewall." Select the "Firewall Options..." section and check the "Enable Stealth Mode" box. This option makes your Mac appear invisible on the network by no longer responding to pings that attackers can use to detect your Mac. It also prevents your Mac from responding to connection attempts.