The Simple Two Clicks Free Solution for Basic Home PC Security
1) Download and install Free Avast Antivirus http://www.avast.com/eng/download-avast-home.html
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2) Turn on Windows Firewall
To Enable Windows Firewall on Windows XP SP2
1. Click Start, click Run, type Firewall.cpl, and then click OK.
2. On the General tab, click On (recommended), and then click OK.
You're done. Two clicks and good luck.