Venezuelans who want to reach such sites have had to use proxy services, which have long been employed by people in China and Iran to circumvent government censorship.
The international director of the Electronic Frontier Foundation, Danny O'Brien, said he thought the Venezuelan net censorship has been "somewhat haphazard and arbitrary."
Nearly half Venezuela's population relies on government-controlled media as its sole information source, the rest on the Internet.
But cutting off Internet is not smart political strategy, said O'Brien.
"I think the important lesson people should learn from these Internet blackouts is that they just throw fuel on the flames of civil unrest," he said.