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Over the last week or two there’s been an increase amount of chatter on forums and blogs about invalid clicks and AdSense. Some of the talk has contained information that has been a little confusing and perhaps even ill-informed (and some ‘influenced’ by companies with their own agendas) - so I got in touch with AdSense and asked if they had any information to help their publishers protect themselves against invalid clicks.
The following is what they replied with - in their words it is ‘a concise guide to how to prevent and monitor invalid clicks, and keep an AdSense account in good standing.’ I hope that it is helpful to AdSense publishers everywhere:
The Google AdSense team has heard many concerns about how Google treats invalid click activity on publisher’s sites, and there have been questions on how to keep your AdSense account in good standing. The Google Ads Quality Traffic Team wants to help all publishers keep their accounts in good order, so here are some tips to keep in mind.
We understand that it’s not always possible to control the behavior of your users, but you can be proactive about monitoring your traffic, and you can take steps to ensure that your site provides a helpful and safe environment for users and advertisers. Here are some top tips for keeping your account in good standing (which you may have seen before): https://www.google.com/adsense/support/bin/answer.py?answer=23921
Expanding on the tip “Be aware of how your site is promoted.” we’d like to remind you that, should you purchase traffic to promote your site, you do so at your own risk. There are many site promotion services out there that appear to be legitimate PPC advertising companies or search engines, but actually may be sending artificial traffic to your site for their own gain. (For legal reasons, we’re not allowed to disclose the names of such services.)
To combat this, we highly recommend that you use channels to segment your traffic by source (e.g. a channel for your site’s Google AdWords traffic only). If one channel’s reports look particularly suspicious, you may want to consider unsubscribing from that traffic service. We also recommend using Analytics to slice and dice your traffic reports further to ensure that you’re receiving clicks from users who are genuinely interested in your ads.
Though we encourage you to be proactive about monitoring your site and ad traffic, we highly discourage the use of click tracking via third-party software or custom ad implementations. These methods may:

• inadvertently disclose sensitive information about you or your site to a third-party
• disrupt Google’s ad delivery or click logging in a way that violates our Terms and Conditions