A virus scanner will only detect known viruses. The hack you mentioned could do anything it wants and no scanner will detect it, because it isn't a virus, it's built in. The only way I could trust it is with a third party checksum like Linux distros use, and the hack came as source code you compiled yourself.
I agree with you about pricing and piracy, I felt really ripped off paying $125 for XP that was a must-install because I lost my driver disks and no W98 drivers were available after my daughter installed XCP from a Sony-BMG music CD she'd bought from the record store she worked at (she's at gamestop now and looking for a different occupation, she thinks gamestop is dying and she's probably right). That much cash for an OS that lacks features other OSes have, even previous versions of Windows, is a double ripoff.
After paying that much for XP and the first upgrade download replaced a perfectly functional LAN driver with one that was completely nonfunctional was the straw that broke the camel's back and drove me to Linux. Of course, if my occupation was fixing customers' Windows PCs like yours is it would be quite different.