SAN FRANCISCO — The F.B.I.’s arrests of 14 people last week were the most ambitious crackdown yet on a loose-knit group of hackers called Anonymous that has attacked a string of government agencies and private companies over the last eight months.

But at least some of the suspects are not your typical hard-core hackers, judging from interviews with two of them and the online traces of others. Some did not bother to cover their digital tracks as they participated in what they saw as an online protest. And some say they were unaware that their feverish clicks on a home computer may have been against the law.

The suspects, mostly in their 20s and living unremarkable lives in small towns and suburbs across the country, now face up to 15 years in prison. Among them are a college student, an ex-Marine, a couple of self-taught computer programmers, even a young man whose only celebrity before last week’s arrest was that he dressed up as Harry Potter for a movie premiere.

While federal law enforcement officials are clearly keen to quash the notion that online attacks are a form of social protest, the arrests highlight a far bigger challenge facing the authorities as they try to stop digital raids carried out by a large and ideologically motivated group of people scattered across the globe.