Yep after viruses, trojan, malware and spyware comes a new menace - Rootkits. These things actually change the way your operating system works so that your normal spyware/malware detectors can't pickup any problematic proggies running on your system. These things are real nasty and apparently the only solution to really get rid of one is to format the system again. There are a few programs out there that will help you detect these bothersome things.
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Tech Support Alert