(By Denis Greenan) Rome, May 17 - Police on Friday arrested four Italian members of the international 'hacktivist' network Anonymous for allegedly hacking into computer systems of the government, parliament and the Vatican. The four also allegedly got into the systems of key infrastructure and major firms but police have not yet said what damage they did. Raids were carried out "across Italy", police said. "The group carried out a series of attacks against the computer systems of critical infrastructure, institutional sites and important companies", police said. Police said the four were a 43-year-old man from near Lecce, in southern Italy, a 20-year-old from Bologna, in central Italy, a 28-year-old from the province of Venice and a 25-year-old from the province of Turin. "They acted under the cover of Anonymous", police said. Anonymous, a digital activism umbrella group linked to numerous high-profile cyber attacks worldwide, has stepped up a campaign in Italy over the last two years. In April hackers from the group brought down the home pages of the Italian interior ministry, the police and the Carabinieri. In a statement circulated online, the hackers said operation 'Tango Down' was a counterattack for a list of grievances including labour injustice in Italy and police brutality at protests in Genoa in 2001 surrounding the G8 summit. Hackers under the same moniker successfully took down the Vatican home page twice in March. In July 2011 Italian police arrested the leader and several group members of a computer hacker cell in Italy tied to Anonymous. Investigators charged 15 people, five of whom were minors, after conducting 32 raids across the country and one in Switzerland, confiscating dozens of computers and other equipment. Police said that the leader of the group was a 26-year-old Swiss-Italian who went by the nickname of "Phre". The cell was accused of carrying out attacks on the Italian Senate, House and central government, as well as targeting other Italian organizations such as AGCOM, the national communications regulatory body; energy giants ENEL and ENI; state broadcaster RAI; and Mediaset, the country's largest commercial broadcaster, owned by Premier Silvio Berlusconi. Anonymous came to world prominence in December 2010 when thousands of supporters downloaded its attack software to defend WikiLeaks, the whistle-blowing website founded by Julian Assange. A group claiming to be connected to Anonymous took responsibility for hacking the Fox News Twitter account to say that American President Barak Obama had been assassinated while campaigning for re-election. Many Anonymous affiliates have taken revenge on the websites of companies, organizations, and government bodies they feel have unfairly treated Assange and WikiLeaks, which released hundreds of thousands of confidential cables about the wars in Iraq and Afghanistan, as well as the inner-workings of US diplomacy around the globe. A typical cyber-assault from Anonymous is called a denial-of-service attack, in which hackers clog a website with too much activity, either shutting it down or rendering its services virtually unusable. MasterCard's website received a denial-of-service attack in December 2010 after it had stopped processing donations to WikiLeaks. PayPal, Visa and a legal office prosecuting Assange suffered similar attacks as part of what Anonymous called Operation Payback. The Italian cell carried out dozens of attacks from January to July 2011. Anonymous, a loose international association of hackers, has staged a string of other well-publicized hacks and attacks on government, religious, and corporate websites. Dozens of people have been arrested for involvement in Anonymous cyber-attacks, in countries including the US, UK, Australia, the Netherlands, Spain, and Turkey. Supporters have called the group "freedom fighters" and digital Robin Hoods while critics have described them as "a cyber lynch-mob" or "cyber terrorists". In 2012, Time called Anonymous one of the "100 most influential people" in the world.