Digital activists linked to the Anonymous collective, a disparate cohort of hackers from around the world, have claimed responsibility for a fresh wave of cyberattacks against a number of Spanish government websites as part of a pro-Catalonia protest campaign.

Multiple accounts with Anonymous' signature Guy Fawkes masks have been tweeting hashtags in recent weeks including #opCatalunya, #FreeCatalonia and #OpSaveCatalonia. They claimed, using screenshots as evidence, to have taken several state websites offline.

The website of Spain's Ministry of Public Works and Transport was hacked to display a "Free Catalonia" slogan, while the homepage of its constitutional court – which ruled the referendum illegal on 17 October – was forced offline on Saturday (21 October).

Anonymous uses distributed denial of service (DDoS) cyberattacks to overwhelm targeted website servers with traffic and force them offline.

While this is not considered a sophisticated form of attack, it can be difficult for websites to combat.

In most cases, hackers use this to stage digital protests, often in support of political causes.

"We are aware of the announcement from Anonymous but we do not know the origin of the attack," a constitutional court spokeswoman told AFP, adding that other IT systems were not affected.

On Friday (20 October), Spain's Department of National Security (Departamento de Seguridad Nacional) warned potential targets that the collective may strike.

"Hacktivist group Anonymous, through associated Twitter accounts, is announcing a massive cyberattack for tomorrow," the DSN wrote in a statement at the time. "In the last few weeks, state websites have received different cyberattacks under the same slogans."

The attacks appear to be ongoing. One of the latest statements now in circulation is a "support request" from a branch of the group called "Anonymous Catalonia".

It reads: "In the name of all the Catalan independence and democracy, Anonymous Catalonia asks all the Anons of the world who are in favour of the freedom of expression [...] and peaceful dialogue to persist in the #FreeCatalonia operation until 29 October 2017."

The call to arms first appeared online on Monday (23 October) however, many Anonymous accounts have been sharing a protest video first published to YouTube in late-September.

"We wish to state that the Catalan people's desire to express their will via a referendum is the majority view and cuts across all strata of society," an individual in the video states.

On 21 October, after a cabinet meeting, Spanish prime minister Mariano Rajoy stated that he wanted to obtain the direct power to dissolve the Catalan government. As reported, he said that assuming more control was needed to "restore order" after the independence attempt.

Hitting back, Catalan president Carles Puigdemont asserted that the unprecedented move would be considered an "attack on democracy". At the same time, hundreds of thousands of protesters hit the streets of Barcelona draped in Catalonia flags, with many chanting for freedom.

The results of the referendum was released on 1 October, with 90% voting in favour. The turnout was approximately 42% and came amid reports of a violent police operation in the region.