To check the status of your firewall and turn it on if needed, follow these steps:
Open Windows Firewall by clicking the “Start” button, clicking “Control Panel,” clicking “Security,” and then clicking “Windows Firewall.”
(If your Control Panel is set for category view, you will see “system and security” but if it is set for large or small icons, then you will actually see “Windows Firewall” itself. That setting is in the upper right hand corner of the Control panel box.)
Click “Turn Windows Firewall on or off.” If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
Click “On,” and then click “OK.”
If you want the firewall to block everything, including the programs selected on the Exceptions tab, select the “Block all incoming connections” check box.
For Mac OS X 10.6 and later
From the Apple menu, select “System Preferences…” When the System Preferences window appears, from the View menu, select “Security & Privacy” (10.7 and later) or “Security” (10.6).
Click the “Firewall” tab.
If the orange padlock icon in the lower-left side of the window is closed, click it, and then authenticate with your Mac’s administrator username and password. This will allow you to make changes.
Click “Turn ON Firewall” (10.7 and later) or “Start” (10.6) to enable the firewall.
To configure the firewall, click “Firewall Options…”(10.7 and later) or “Advanced…” (10.6). In the sheet that appears, choose from the following options:
For the strictest setting, check “Block all incoming connections.”
Check “Automatically allow signed software to receive incoming connections” to allow digitally signed applications access to your network without prompting.
Click “Enable stealth mode” to have your computer ignore pings and similar software that attempts to discover your computer.
Use the plus and minus buttons to add and remove applications from the firewall. When added, you can either allow or block traffic to them.