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kaled - 6:14 pm on Dec 14, 2009 (gmt 0)
You need a full anti-virus solution - try AVG (free edition). Kaled.
Defender is not adequate, not even close.
You need a firewall. The standard XP firewall can block intrusions (as might a firewall in your router) however, a firewall that blocks outgoing connections to the internet is advisable - try ZoneAlarm (free edition).