A 27-year-old man described as one of the world's most prolific spammers was arrested Wednesday in the U.S., and federal authorities said internet userscould notice a decrease in the amount of junk e-mail.

Robert Alan Soloway is accused of using networks of compromised "zombie" computers to send out millions upon millions of spam e-mails.

U.S. attorney Jeff Sullivan said the case is the first in the country in which federal prosecutors have used identity theft statutes to prosecute a spammer for taking over someone else's internet domain name. Soloway could face decades in prison, though prosecutors said they have not calculated what guideline sentencing range he might face.

"He's one of the top 10 spammers in the world," said Tim Cranton, a Microsoft Corp. lawyer who is senior director of the company's Worldwide Internet Safety Programs group. "He's a huge problem for our customers. This is a very good day."

Zombiesare computers that have been hijacked to perform commands and functions issued to them by the attackers, often without the owners' knowledge.

A U.S. federal grand jury last week returned a 35-count indictment against Soloway charging him with mail fraud, wire fraud, e-mail fraud, aggravated identity theft and money laundering.

Soloway pleaded not guilty Wednesday afternoon to all charges after a judge determined that— even with four bank accounts seized by the government— he was sufficiently well off to pay for his own lawyer.

He has been living in a ritzy apartment and drives an expensive Mercedes convertible, said prosecutor Kathryn Warma. Prosecutors are seeking to have him forfeit $773,000 US they say he made from his business, Newport Internet Marketing Corp.

A public defender who represented him for Wednesday's hearing declined to comment.

Man accused of running network of zombies

Prosecutors say Soloway used computers infected with malicious code to send out millions of junk e-mails since 2003. The computers are called "zombies" because owners typically have no idea their machines have been infected.

Zombie computers are typically organized into networks called botnets, and used to distribute spam or phishing e-mails,as well asviruses and Trojans that are used to hijack other computers. Botnet operators often rent time or bandwidth on their networks to spam e-mail marketers and phishing scam artists.

He continued his activities even after Microsoft won a $7-million US civil judgment against him in 2005, and the operator of a small internet service provider in Oklahoma won a $10-million judgment, prosecutors said.

The investigation began when the authoritiesstarted receiving hundreds of complaints about Soloway, who had been featured on a list of known spammers kept by The Spamhaus Project, an international anti-spam organization.

The Santa Barbara County, Calif., Department of Social Services said it was spending $1,000 a week to fight the spam it was receiving, and other businesses and individuals complained of having their reputations damaged when it appeared spam was originating from their computers.

"This is not just a nuisance. This is way beyond a nuisance," Warma said.

Soloway used the networks of compromised computers to send out unsolicited bulk e-mails urging people to use his internet marketing company to advertise their products, authorities said.

People who clicked on a link in the e-mail were directed to his website. There, Soloway advertised his ability to send out as many as 20 million e-mail advertisements over 15 days for $495, the indictment said.

Soloway remains in federal detention pending a hearing Monday.