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The ethics of the Internet dictate that you crawl politely, obey robots.txt and properly identify yourself This isn't a new issue. Link networks and sites have blocked crawlers and manipulated Google for years. Fortuneatly, it's only a small fraction of the web. Also, it unlikely links from those networks have much value, so crawl priority would be super low anyway. Actually, it could be viewed as beneficial when blackhat sites block OSE and aHrefs, because those sites often get penalized by Google, but 3rd party crawlers have no way to know this, so blocking effectively keeps them out of the indexes.