Four keyphrases, four ads clicked within 34 seconds

Now here is a classic click fraud symptom. This user at 172.24.6.31 used a proxy server at a Level3 site 65.57.245.11 in San Francisco to find four of our ads and click them within seconds.

Update: The "cuplrit" was Google. Apparently the Adwords people use this IP address when checking your ads. :) The official answer from Google about these clicks was some boilerplate answer which said how wonderful their system is, but nothing specific.