A two-click penalty is a method that Google uses to prevent click fraud.
If Google suspects that clicks on display ads on a website are frequently fraudulent or accidental, it may implement a “Two-Click Penalty”.
When this happens, when people click on an ad on that site, an overlay will appear, asking them to “Click to go the site” (or similar). This means that ads need two clicks to get someone to the site.
This, of course, reduces the amount of traffic that ads send (legitimately or otherwise) and so also reduces revenue from those ads (which is why it’s called a penalty).
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