Use a Firewall
If a computer is ever connected to a network or the Internet, it should always have a firewall installed and running. This filters what type of traffic is allowed into the computer, thus stopping hacker attempts if properly configured. Since Windows XP, Microsoft has included Windows Firewall by default. From the Control Panel, open the firewall settings and make sure it is enabled. Plus, make sure any exceptions that are checked are for legitimate programs and are necessary. If you have a third-party firewall installed, such as an anti-virus package, you probably want to disable Windows Firewall, or vice-versa, so only one is active.