Came back and realized I should have worded that second sentence better. Field didn't fail to defend his copyright. He put the files up in January, filed copyr

Came back and realized I should have worded that second sentence better. Field didn't fail to defend his copyright. He put the files up in January, filed copyrights with the Copyright office, waited for them to be indexed and cached, and sued Google in April. He protected his copyright about as vigorously as you can with the available legal tools. The question of implied license in this case is whether putting something on the internet without taking steps to stop search engines from indexing+caching it constitutes an implied license. The court ruled it did, but it relied in part on Field taking specific actions to allow it (such as the robots.txt file), so it's not entirely clear that in a different case they would rule the same way. If someone put up a site with just a plain text file without HTML tags and no robots.txt file maybe the court would rule that there was not an implied license there, I don't know. They also took into consideration that there are well-known industry standard ways of preventing Google and others from indexing and caching your site, so maybe they would consider that alone sufficient to rule that there's an implied license if you don't follow the industry standards. In any case, Field v. Google has little-to-nothing to do with failing to defend a copyright.