Federal prosecutors credited the man responsible for transmitting the Melissa virus - a computer bug that did more than $80 million in damage in 1999 - with helping the FBI bring down several major international hackers.
Court documents unsealed Wednesday at the request of The Associated Press show that David Smith began working with the FBI within weeks of his 1999 arrest, primarily using a fake identity to communicate with and track hackers from around the world.
"Smith provided timely, substantial assistance to the United States in the investigation and prosecution of others," New Jersey's U.S. Attorney, Christopher J. Christie, wrote to federal judge Joseph Greenaway in an April 2002 letter.
Greenaway, who could have sentenced Smith to about 10 years in prison under federal sentencing guidelines, reduced the sentence to 20 months after reading the letter.
The 35-year-old Smith, who declined to be interviewed, is serving his sentence in federal prison at Fort Dix, N.J. His attorney did not return calls from the AP.
According to the court document, Smith helped the FBI bust virus senders abroad and stop viruses in the U.S.
The letter says that two months after his arrest, Smith gave the FBI the name, home address, e-mail accounts and other Internet data for Jan DeWit, the author of the so-called Anna Kournikova virus in the Netherlands. The FBI passed the information on to authorities in the Netherlands. DeWit was arrested and later sentenced to probation.
Also in 2001, Smith recorded online discussions with Simon Vallor, the author of the "Gokar" virus that infected Microsoft computer systems worldwide. The FBI contacted detectives in the United Kingdom, who arrested Vallor early the next year.
Vallor, 22, was sentenced to two years in jail after pleading guilty in London to writing and distributing "Gokar" and two other viruses.
The federal prosecutor also said that Smith was working with the FBI to develop an investigative tool that theoretically could help identify an e-mail sender who was trying to mask his or her identity.
Smith began cooperating with the FBI immediately after his arrest. He told the judge while pleading guilty that he did not expect the amount of damage that took place.
"When I posted the virus, I expected that any financial injury would be minor and incidental," he said. "In fact, I included features designed to prevent substantial damage."