Government censorship of the Internet is a cat-and-mouse game. And despite more aggressive tactics in recent months, the cats have been largely frustrated while the mice wriggle away.

But this year, the challenges for Silicon Valley will mount, with Russia and Turkey in particular trying to tighten controls on foreign-based Internet companies. Major American companies like Facebook, Twitter and Google are increasingly being put in the tricky position of figuring out which laws and orders to comply with around the world — and which to ignore or contest.