How do you prevent invalid clicks and page impressions?

Google strictly prohibits any method used to artificially generate clicks or page impressions and closely monitors activity using engineering systems and human analysis.

Google's proprietary technology analyzes clicks and impressions to determine whether they fit a pattern of use intended to artificially drive up an advertiser's clicks or impressions, or a publisher's earnings. Our system uses sophisticated filters to distinguish between clicks generated through normal use by users and clicks generated by unethical users and automated robots, enabling us to filter out most invalid clicks and impressions. Advertisers are not charged for the clicks and impressions we filter out.

In addition to our automated system, we have a team dedicated to detecting invalid activity using several specialized tools and a wide variety of techniques based on extensive experience tracking and monitoring user behavior and analyzing scenarios. We continually upgrade our detection mechanisms to proactively combat invalid activity.