analyze what happens. You can compare normal behavior - time on page, number of pages viewed etc occurring from normal organic traffic against traffic generated by the ad campaign. Did one site or group of sites send 90% of your clicks, but almost zero real traffic?
Another thing I've seen happen through Adwords was a large percentage of traffic coming through with default language set to Arabic and spending 0 time on site. (on a site intended for English speakers)
content on 3rd party site->ad->your landing page.
analyze what happens. You can compare normal behavior - time on page, number of pages viewed etc occurring from normal organic traffic against traffic generated by the ad campaign. Did one site or group of sites send 90% of your clicks, but almost zero real traffic?