GP didn't ask about liability for reading it but rather the legality of intentionally retaining a local copy. Intentionally making a copy of content which you know you don't have a license for is against copyright law in all western jurisdictions that I'm aware of.

Reading something isn't inherently illegal itself, true. I'm fairly certain that intentionally navigating to a website that you know contains pirated content is a violation of copyright law though. (Of course no one is going to bother prosecuting you for it, but still.)

The laws surrounding classified information in the US are quite different from copyright law. They aren't relevant here at all. (https://en.wikipedia.org/wiki/Classified_information_in_the_...)