Leonard0 - 12:49 pm on Oct 14, 2011 (gmt 0)
IMO, your greatest danger is from the traffic that is sent from the PTC site, not from ads on unauthorized sites. You are protecting advertisers with the unauthorized sites list but not from the traffic to your site who are most likely clicking like crazy. Google is probably filtering most of those clicks but it will set off red flags.
My advice is to either block that traffic or take the drastic measure of removing ads from the landing page temporarily.
Check your Adsense report to see if there is an unexpectedly high amount of traffic from a particular country. Then you could block the country by IP range. If you use DFP, you may be able to target that country with non-Adsense ads.
If you can't remove ads from your pages, you could take your site off the authorized sites list until you get something worked out. That will show Google that you are not involved in a click scheme. Otherwise you could receive the dreaded email about your site presenting significant risk to advertisers.