SAN FRANCISCO — In the most visible law enforcement response to a recent spate of online attacks, the Federal Bureau of Investigation on Tuesday announced the arrests of 16 people across the country in connection with strikes carried out by a loose, secretive federation of hackers called Anonymous.

In an indictment unsealed Tuesday afternoon in United States District Court in San Jose, Calif., 14 people were charged in connection with an attack on the Web site of the payment service PayPal last December, after the company suspended accounts set up for donating funds to WikiLeaks. The suspects, in 10 separate states, are accused of conspiring to “intentionally damage protected computers.”

Anonymous had publicly called on its supporters to attack the sites of companies it said were turning against WikiLeaks, using tools that bombard sites with traffic and knock them offline.

A Florida man was also arrested and accused of breaching the Web site of Tampa InfraGard, an organization affiliated with the F.B.I., and then boasting of his actions on Twitter. And in New Jersey, a former contractor with AT&T was arrested on charges that he lifted files from that company’s computer systems; the information was later distributed by LulzSec, a hacker collective that stemmed from Anonymous.