Google Adsense will never put 'spyware' on your PC... It MIGHT put a cookie on your machine if the ads are CPA (Cost Per Action) rather than CPC (Cost Per Click). The CPA Ads are ones where you click on something and the advertiser doesn't get a penny until you DO something (eg, buy the TV, Register as a subscriber, etc). This means the payouts are less frequent but MUCH higher in value (I've seen sites offering $30 per action). For the CPA action to work, Google uses a cookie on your machine to see if you do the action within 30 days of clicking.
At the end of the day, its not a big brother thing - its Google trying to find a fair way of paying its advertisers.
Alternatively, it could be that you're using an insecure browser and you are visiting sites which exploit it...
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