1. Trojan Guarder Gold Version (or any other trojan remover)
2. Webroot Spy Sweeper (or Spybot or any other spyware remover; there is a online one http://www.spywareguide.com/txt_onlinescan.html?)
3. Install an Antivirus software such as McAfee (Noton not recommended cause no way to remove it completely)
4. Install Zonealarm Pro
Perform the security check at least once a week and update the database.
Good luck!