SEATTLE -- A 27-year-old man described as one of the world's top spammers was arrested Wednesday, a development that federal authorities said could lead to an immediate, perceptible decrease in the amount of junk e-mail winging its way across the Web.

"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. "He's a huge problem for our customers. This is a very good day."

Robert Alan Soloway's arrest came a week after a federal grand jury returned a 35-count indictment charging him with mail fraud, wire fraud, e-mail fraud, aggravated identity theft and money laundering. He's accused of using networks of compromised computers to send out millions upon millions of junk e-mails since 2003. He continued his activities even after Microsoft won a $7 million civil judgment against him in 2005 and Robert Brauer, the operator of a small Internet service provider in western Oklahoma, won a $10 million judgment, prosecutors said.

U.S. Attorney Jeff Sullivan said Wednesday 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, and it would mean at least an extra two years on Soloway's sentence if he is convicted. He could face decades in prison, though prosecutors said they have not calculated what guideline sentencing range he might face.

In court Wednesday afternoon, Soloway pleaded not guilty 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 at the ritzy Harbor Steps apartments near Pike Place Market and drives an expensive Mercedes convertible, said Assistant U.S. Attorney Kathryn Warma. Prosecutors are seeking to have him forfeit $773,000 they say he made from his business, Newport Internet Marketing Corp.

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

The investigation began when the Federal Trade Commission, Better Business Bureau and Washington state attorney general's office began 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 networks of compromised computers called "botnets" to send out unsolicited bulk e-mails urging people to use his Internet marketing company to advertise their products. People who clicked on a link in the e-mail were directed to his Web site, where he advertised two types of services. In one, he would agree to send out as many as 20 million e-mail advertisements over 15 days for $495, the indictment said.

In another, he would offer to sell software that the buyer could use to "broadcast" e-mails to 80 million e-mail addresses. He falsely claimed the e-mail addresses were all legal, "opt-in" addresses of people who had chosen to receive the solicitations, and at any rate the software he sent typically didn't work, according to the indictment.

The Spamhaus Project rejoiced at his arrest.

"Soloway has been a long-term nuisance on the Internet - both in terms of the spam he sent, and the people he duped to use his spam service which has, in many cases, got them into trouble," organizers wrote on spamhaus.org.

Soloway remained in federal detention pending a hearing Monday.