I have never ever put an ad anywhere without a channel. Not once since day one. I'm not changing my ads, I tweaked them a couple times and that's it. Always worked great. Recently I noticed I'm getting a couple clicks on an ad without a channel. It only lists them when looking at aggregated data. I looked at some wider stats and it seems I had ~25 a month of those mysterious clicks. I have AdSense on 2 blogs and one site. Never had AdSense anywhere else. All my ads have channels (just 6, 2 per page cause I'm using just 2 ad units per page). I see impressions and clicks on all my channels, so they're properly displayed. I have not edited my AdSense code, ever. Someone took my code, removed the channel data and displays my ads or could there be some other reason? PS. It started in December it seems