More than 1 million people in Cuba per day are using an anti-censorship tool supported by the U.S. government to evade government blackouts of social media such as Facebook.

Censorship-circumvention software company Psiphon says it has facilitated the transfer of over 600 terabytes of data from users in Cuba since Sunday, when many social media sites stopped working in the country.

Psiphon uses proxy servers that disguise internet traffic so that it flies under the radar of many censorship methods. The Toronto-based nonprofit has received funding from the Open Technology Fund, a U.S. government nonprofit that aims to support global internet freedom technologies. Republican Sen. Marsha Blackburn praised the technology in a Tweet on Friday.

On Thursday, President Joe Biden said the U.S. is examining whether it’s able to restore internet access shut down by the Cuban government.

Similar spikes in the use of Psiphon have been observed after the government of Belarus shut down access to much of the internet during elections last year. The service is also popular in Myanmar, where the internet is highly restricted.