As a side-note, I can at least tell my experience with basically the same thing, I think.
Last Saturday, I was almost finished installing/customizing a new computer for my church. Well, right at the very end, Micro Antivirus 2009 showed up out of the blue on the computer, and gave some warning/error messages and all.. icon in the task tray.
Anyhow, I think I got rid of it pretty quickly by just looking for suspicious tasks, and killing them, and at the same time, letting both Windows Defender and AVG 8 remove everything they found, including a reboot required by AVG to remove some. After the reboot, there was an AV icon on the desktop as well as a dirty pictures link or something like that. I manually deleted those, and it seems everything was clean.
But I don't like to assume anything, and since it was a new setup and for our church, I decided I'd just go ahead and wipe the whole thing and reinstall again. I'd hate for something to pop up 3 months down the road knowing I coulda zapped it from the get go.
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"If to err is human, then I must be some kind of human!" -Me