The crackdown came — but even the most skeptical Catalans failed to anticipate how sweeping it would be. For weeks in advance of the Oct. 1 referendum, Spanish courts issued a flurry of orders shutting down websites that had something to do with the vote. Telecom companies received instructions to shut off user access to information sources provided by the Catalan government. And at one point in September, the Spanish police even shut down the entire “.cat” domain by occupying the offices of its registry and arresting its head, whom they kept in custody for three days. He’s now facing sedition charges.

Not all the measures were official. Anonymous hackers shut down some pro-independence sites with DDoS (distributed denial of service) attacks. Others tried to use a spam bombardment to disable an email account used by Catalonian mayors to coordinate the vote.

And as for that referendum app? After Spanish officials learned about it, a court order was sent to Google Play, the Android-based app store, demanding its removal — and the Americans complied. “I’m a tech guy,” says Jordi Puigneró, chief technology officer of the Catalonian government. “So I’ve always been a great fan of Google and its principles of respect for digital rights. But now I’m really disappointed with the company.” (Puigneró’s office was also occupied by police during the referendum, he says.)

Spain’s heavy-handed police response to the referendum, which injured almost 900 people, ended up dominating the headlines. Yet the remarkably bitter cyber-conflict between Madrid and Barcelona has received far less attention — despite its potentially far-reaching implications.

Jeremy Malcolm of the Electronic Frontier Foundation, a group that monitors freedom of expression online, was surprised at the aggressiveness of the Spanish government’s online measures to suppress the vote: “It’s really quite unusual to see this kind of crackdown on political speech and democratic representation in a country that purports to uphold rights like Spain does.” Especially remarkable, he says, was the broad nature of the central government’s online offensive, which entailed shutting off entire swaths of the Internet. He says that Madrid’s cyber-campaign reminds him less of a liberal democracy than countries “that are under military rule or have an autocratic government.”

He hopes, he says, that Catalan activists will go forward with their vow to take the Spanish government to the European Union Court of Human Rights over its suppression of online freedoms.

A spokesperson for the Spanish Embassy in Washington had this comment: “No domain or website was closed in Spain in violation of the freedom of expression. The websites were closed because they were used to facilitate the illegal vote, providing detailed instructions and practical information. … In Spain, many websites and magazines openly advocate for independence and secession under the full protection of the law. Aside from the illegal referendum’s official websites, no other websites were closed.”

The Catalans received some unexpected (and unsolicited) help from Julian Assange, operating from his base in the Ecuadoran Embassy in London. His efforts were bolstered by an army of mysterious social media bots and Russian-sponsored media outlets. It is by now well-known that Moscow’s troll armies have a special weakness for separatist groups of all kinds, since they see them as drivers of fragmentation and instability. They may not be entirely wrong. The Catalonian leadership’s push for independence is currently shaking Spain like few other events in recent memory.

Guillem Colom, an analyst at Spanish think tank Thiber, said that “hacktivists” from such groups as LulzSec, Anonymous and AnonPlus also staged attacks in the Catalans’ name, blocking or defacing sites connected with the government and the security forces. The Spanish section of Reporters Without Borders has harshly criticized Catalonian government supporters “for unprecedented harassment [of journalists] by the authorities and on social networks.”

The regional government’s primary task was a fairly straightforward one: to provide citizens with information about the referendum. Voters in western European countries usually don’t have to worry about going to the polls in defiance of their own governments. But the Spanish authorities had made it clear that they were willing to deter the vote even if that meant physically capturing and holding polling stations.

On the day of the referendum, the Catalonian government launched a system designed to help voters find alternate polling stations in case their own were closed by the police. They set up a robust system of backup servers, activating a new one every hour. Their paranoia was justified: As soon as polling began, hackers launched a series of ferocious attacks to bring the system down. The Spanish police also tried shutting down the wireless Internet access of polling stations, prompting crowds in the streets to start up one of the oddest political chants in recent memory: “Airplane mode!” (They were calling on cellphone users to free up extra bandwidth for polling officials).

Despite it all, regional officials did manage to keep the referendum going. By the end of the day, 2.26 million citizens of the region had taken part. (That represented a turnout of 42.3 percent of Catalonia’s 5.34 million voters, just over 90 percent of whom voted yes.) Catalan officials deem that a satisfactory result, considering the scale of the central government’s campaign to prevent the vote from happening. But critics of the referendum, citing the relatively low turnout, say that the result is still far from a clear mandate for secession.

The political passions stirred up by the referendum haven’t abated. This week, Madrid arrested two leading Catalan separatists, fueling fresh demonstrations in Barcelona.