"Many of these are just a few frustrated high school students with a Web site. But as we continue to see, others have the potential to be dangerous," said Mary Bossi, a terrorism expert in Greece, The Washington Post reported Saturday.
In Greece, which has been close to bankruptcy and may require a second international bailout -- on top of a $170 billion loan already granted by the European Central Banks, the European Union and the International Monetary Fund -- a group called "I Won't Pay," now claims to have 10,000 supporters.
Part of the group's tactics is to vandalize government projects and refuse to pay a variety of fees from highway tolls to hospital bills, the Post said.
Another group, called the Anti-Establishment Movement, has 7,000 members, up from about 2,500 two years ago. One of the group's strategies is the use of firebombs during anti-government protests, the newspaper said.
Anti-government groups have also gained strength in Britain, where a North London group called UK Uncut has advocated for civil disobedience to protest government spending cuts.
"There is a sense of general injustice, that the government bailed out capitalism and the citizens are footing the bill while the capitalist system is running like nothing ever happened. And yet things have happened. There are more taxes, less services, and anger is emerging from that tension," said Bart Cammaerts, an expert in anti-government groups at the London School of Economics.