London (CNN) -- An 18-year-old man has been arrested in Scotland on suspicion of being linked to computer hacking groups Anonymous and LulzSec, police in London said Wednesday.
Officers from the Metropolitan Police said the suspect uses the online nickname "Topiary" and has acted as a spokesman for both groups.
He was detained in the isolated Shetland Islands, off northern Scotland, and is being brought to central London, a statement on the police website said. The home where he was found is being searched.
"The man arrested is believed to be linked to an ongoing international investigation into the criminal activity of the so-called 'hacktivist' groups Anonymous and LulzSec," police said.
A 17-year-old male is also being questioned in connection with the inquiry, police said, and a house in Lincolnshire is being searched.
The arrests are part of an ongoing investigation into network intrusions and "denial of service" attacks -- which overload a website's server -- against a number of international businesses and intelligence agencies, police said.
Hacking groups such as Anonymous and LulzSec have claimed a number of high-profile attacks in recent months, stealing information from the U.S. Senate and Arizona state police websites, as well as data from major corporations like Sony, Bank of America and Nintendo.
They've also successfully blocked access to the websites of Visa, MasterCard, the CIA and, most recently, several News Corp. newspaper websites.
On Tuesday, Anonymous, which supports the controversial whistleblower site WikiLeaks, posted an "official communique" to PayPal and its customers, urging people to close their accounts with the online payment service.
The hacker collective accuses PayPal of being unfair for refusing to allow donations to WikiLeaks and for helping law enforcement track down hackers.
Police in Britain, the United States and elsewhere have made a number of arrests of suspected "hacktivists" in recent weeks.
Following two earlier arrests, a 19-year-old man has been charged and is due to appear in court in the UK in late August, and a 16-year-old boy is scheduled to return in late August, pending further inquiries, police in London said.
A post on LulzSec's Twitter feed last Thursday linked to a joint statement from it and Anonymous, apparently responding to comments by the FBI quoted in an NPR article.
The joint statement, addressed to the "FBI and international law authorities," says: "We are not scared any more. Your threats to arrest us are meaningless to us as you cannot arrest an idea.
"Any attempt to do so will make your citizens more angry until they will roar in one gigantic choir."