A theft of computer source code from Cisco Systems, reported a year ago, has led to a wide-ranging investigation of potential criminal activity involving multiple server break-ins in several countries, according to the U.S. Federal Bureau of Investigation (FBI).

Swedish police last week confiscated computer equipment from a 16-year-old during an investigation related to the Cisco theft, according to police officials. The teenager, who the police did not identify, was released to his or her parents. In addition, the U.K.'s Metropolitan Police executed two search warrants in September, and arrested a 20-year-old man. The suspect's computer equipment was confiscated, but he was later released, according to a Metropolitan Police spokesman.

"As a result of recent activities that have taken place, the criminal activity appears to have stopped," said Bill Carter, an FBI spokesman.

Officials with the Metropolitan Police and the FBI said an investigation continues. The FBI, working with law enforcement agencies in several other countries, is looking into "sophisticated" criminal activity involving multiple server intrusions in several countries, Carter said. Carter would not comment on specific attacks.

In e-mail messages sent to a University of California, Berkeley, researcher last year, a computer hacker claimed to have breached the computer networks of several U.S. government sites, including military installations, according to a New York Times story published Tuesday.

After the Cisco source code theft was announced in May 2004, security experts expressed concern that hackers could use the code to look for security holes in Cisco products. Companies using Cisco's networking products often connect them directly to the Internet without firewalls or other security products.

Cisco applauded the Swedish arrest. "We are very encouraged that an arrest has been made in Sweden and will continue to work with the appropriate law authorities," said David Cook, a Cisco spokesman. "We will take every measure to protect our intellectual property and take this issue extremely seriously, as you would expect."