I asked Google for more information on the so-called invalid clicks. Following is the response I just received:
Hello Erik,
As you know, Google treats instances of invalid click activity very
seriously. Due to the proprietary nature of our algorithm, we cannot
disclose any details about how our monitoring technology works or what
specifics we found on your account. However, we can assure you that we
have again reviewed your situation thoroughly and accurately, and could
re-confirm that your account violated our program's Terms and Conditions.
You could view AdSense Terms and Conditions at:
https://www.google.com/adsense/terms
https://www.google.com/adsense/faq
It has come to our attention that invalid clicks have been generated on
the ads on your web pages. We have therefore disabled your Google AdSense
account. Please understand that this step was taken in an effort to
protect the interest of the AdWords advertisers.
A publisher's site may not have invalid clicks on any ad(s), including but
not limited to the use of robots, automated clicking tools, or other
deceptive software. Also, a publisher may not click on the ads on his own
website, or encourage others to do so.
Practices such as these are in violation of the Google AdSense Terms and
Conditions, which can be viewed at: https://www.google.com/adsense/terms .