A day after the authorities arrested several hackers from the Anonymous movement, the director of the Federal Bureau of Investigation, Robert S. Mueller III, warned members of Congress that terrorist groups might use hackers to attack the United States.
"Terrorists have shown interest in pursuing hacking skills," Mr. Mueller said Wednesday in written testimony to a House appropriations subcommittee reviewing the bureau's budget. "And they may seek to train their own recruits or hire outsiders, with an eye toward pursuing cyberattacks. These adaptations of the terrorist threat make the F.B.I.'s counterterrorism mission that much more difficult and challenging."
Mr. Mueller said that the federal government must act swiftly to prevent such attacks and economic espionage from other countries because they pose a "potentially devastating" threat to the country's businesses and infrastructure.
"We tend to focus on protecting our databases, protecting our infrastructure, which is absolutely an appropriate focus," he said. "But we should not forget that you want to identify these individuals who are responsible for these crimes, investigate them, prosecute them and put them in jail for a substantial period of time."
Mr. Mueller has been particularly vocal over the past week about the issue of hacking and cybersecurity. Last Thursday at the RSA computer security conference in San Francisco, Mr. Mueller said that a terrorist had proclaimed in a recruiting video "that cyberwarfare will be the warfare of the future."
Anonymous embarrassed the F.B.I. in February when it posted a 16-minute recording of a conference between the bureau and law enforcement officials in Europe about their joint investigation into the hackers. The group has supported the whistle-blower site WikiLeaks and has claimed responsibility for hacking the Web site of a law firm that represented a Marine accused of killing unarmed civilians in Haditha, Iraq, in 2005.
On Tuesday, federal prosecutors in New York revealed that a leading hacker known as Sabu had been cooperating with the federal authorities, helping them to arrest several "hactivists" for Anonymous in the United States and Europe. Sabu was identified in court papers as Hector Xavier Monsegur, a 28-year-old who operated from a sixth-floor apartment on the Lower East Side of Manhattan.
Mr. Monsegur pleaded guilty in August to dozens of hacking charges. On Tuesday, charges against five others, including a man in Chicago and others in Britain and Ireland, were unsealed by the prosecutors in New York.