What are invalid clicks and how google identifies them ?
Invalid clicks, as defined by Google, are clicks that are illegitimate, unintentional, or resulting from malicious software. The most common examples of this are: Clicks by bots or other automated clicking tools. Manual clicks, used to increase your costs or the profits of websites hosting ads.
Each click on an ad is examined by system, and Google has sophisticated systems to identify invalid clicks and impressions and remove them from your account data.
Google uses real-time detection and filtering systems to examine each click on an AdWords ad. The discarded clicks can be viewed in your Adwords account. Offline analysis - Both automated algorithms and manual analysis are used to detect invalid clicks while offline, and is credited to the advertisers.