The most effective way to protect your PC from outside attack is to install and activate a firewall program. If your PC is running Windows XP, you already have a firewall program installed on your system. To determine if the Windows Firewall is activated on Windows XP Service Pack 2, follow these steps:
Click the Windows Start button and select Control Panel.
When the Control Panel opens, select Security Center from the Category view.
When the Security Center opens, select Windows Firewall.
When the Windows Firewall dialog box appears, make sure the On option is checked.
Click the OK button.