This is a HUGE HUGE HUGE point in favor of open source software. "But legitimate companies wouldn’t try install anything without your permission – they’d lose customers". Adware companies are starting to buy game companies and tack on spyware to their games. This post makes the very good point that lots of adults buy games for kids without knowing the first thing about them, and the kids aren’t necessarily sophisticated enough (or interested enough – not that most adults are either) to read the fine print in the EULAs. Bang! You’ve got an uninterrupted chain from malicious attacker to unsuspecting pawn to mistakenly trusted installer, and there’s your next round of spam zombies.
http://www.gamejournalism.com/archives/2004/Oct/21/adware_firms_expand_foothold_in_gaming.html