People who have smuggled in satellite dishes provide illegal connections to the Internet for a fee or download movies to sell on discs. Others exploit the connections to the Web of foreign businesses and state-run enterprises. Employees with the ability to connect to the Internet often sell their passwords and identification numbers for use in the middle of the night.

Hotels catering to tourists provide Internet services, and Cubans also exploit those conduits to the Web.

Image Yoani Sánchez at her home in Havana, where she writes a blog about daily life that gently critiques Cubas government. Credit... Jose Goitia for The New York Times

Even the country’s top computer science school, the University of Information Sciences, set in a campus once used by Cuba’s spy services, has become a hotbed of cyber-rebels. Students download everything from the latest American television shows to articles and videos criticizing the government, and pass them quickly around the island.

“There is a whole underground market of this stuff,” Ariel said.

The video of Mr. Alarcón’s clash with students was leaked to the BBC and CNN, giving the world a rare glimpse of the discontent among the young with the system. His answers to the questions seemed evasive. Asked about the ban on travel, Mr. Alarcón suggested that if everyone who wished to were allowed to travel, there would not be enough airspace for the planes.

Another event many people witnessed through the digital underground was the arrival in the United States of Carlos Otero, a popular television personality and humorist in Cuba who defected in December while on a trip to Toronto.

Illegal antennas caught signals from Miami television stations, which youths turned into digital videos and shared. Though the event smacked more of celebrity news than politics, it would never have been shown on the official media.