Perhaps you haven't come across any Redirect Notice served by Google, after clicking an ad on its content network. I too hadn't till I decided to click on some of the ads, I manage, to get the feel of customer behavior. To my disbelief, some of the placements (Not All though), serves you notices like I have posted above, just click on them to know what they read. Some ads, after clicking would say "The previous page is sending you to ....., If you do not want to visit that page, you can Return to the Previous Page". Another one says, "The previous page is sending you to an invalid URL, If you do not want to visit that page, you can Return to the Previous Page". I found Url is valid in both the cases, because one of the ad I have myself created, which works well at other places, serves "invalid url" notice. Check your own ad too, Google might be preventing, visitors from reaching your website!
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